Truth be told, I actually want her to return by teaming up with the other antagonists (King Sombra, Gilda, the Diamond Dogs, Ahuizotl, Garble & his dragon gang, Mane-iac, etc) to get their revenge not just on Twilight, Celestia & their friends & family, but the WHOLE of Equestria...
Well, at the very most show has her return to try and ruin the lives of Shining Armour, Princess Cadence & their foals (if they ever have any), before going into a superpowered rage, with her turning into a dragon, finally meeting her end at the hands (or rather, hooves) of Twilight & her friends, courtesy of their newly acquired Rainbow Power...
[Twilight continues pumping more and more magical energy into Rainbow Dash who grows larger and larger. Twilight sweats and starts to show exhausted. Rainbow Dash lets out a huge roar as she grows almost as big as Chrysalis.]
[Twilight collapses under stress and Fluttershy flies to her.]
Fluttershy: "Oh dear, Twilight... that was incredible... but are you all right?"
Rarity: [Trots to Twilight and supports her] "I really hope you know what you are doing dearie..."
Pinkie Pie: [Hopping around, giggling] "Go Dashie! Show that big mean queen!"
Twilight Sparkle: [Exhausted, but smiling] "I hope so too, Rarity... but there was no time to lose."
[Dragon-Chrysalis cringes back at Dash's roar, barely avoiding the cyan drake's snapping jaws]
Dragon!Chrysalis: [Stunned] "But...how?! That's impossible! This kind of transformation can't be done without Changeling magic! Nothing else--not even an Alicorn's magic--should be able to do this!!" [Snarls, flares out her wings] "Well, that's a neat trick, you little brat...but not even YOU can defeat a Queen!"
Dragon!Rainbow Dash: [Looks down at her friends and smirks] "No worries, Rare! I'll have Queen Gruesome taken care of in no ti--"
[Before Dragon!RD can finish her boast, Dragon!Chrysalis zooms forward while she's distracted and slams into her in a full-body tackle, sending the cyan dragoness tumbling off her feet]
Applejack: "LEG IT!!"
[The five mares scramble away just as their transformed friend hits the ground behind them...the impact is nothing short of cataclysmic, kicking up a burst of wind that blows clouds of dust and bits of dislodged earth everywhere, nearly knocking them off their hooves from the shockwave alone as they try to both carry an exhausted Twilight AND dodge the falling debris. The tremendous THUD Dragon!Rainbow makes as she hits the ground is near-deafening, as is Dragon!Chrysalis' evil cackle]
[The five un-transformed mares manage to escape, heading straight for Ponyville. Dragon!Chrysalis pays them no heed]
Dragon!Chrysalis: [Pinning Dragon!RD to the ground, snarling in her face] "Little word of advice: dragons NEVER take their eye of their prey! Then again, I wouldn't expect a boisterous grass-eating pony to know such things!"
Dragon!Rainbow Dash: *Grunts in pain* "I'll admit: Pretty good advice! Here's some from me: Mind your head, QUEENIE!!" [Without a beat, she cranes her neck and head off to one side, then snaps it back forward in a lateral headbutt. Though causing no injuries--her new horns weren't angled right for that--the move makes Dragon!Chrysalis reflexively loosen her grip and cringe back...which gives Dragon-Rainbow the perfect opening to spring off the ground and tail-slap her foe hard enough to knock her aside.]
[Standing at her full height, wings spread and fangs bared, the cyan Dragon-Pegasus gives her challenge]
"So, you say ponies eat grass? Well; how about biting the dust, Chryssie?"
Dragon!Chrysalis: [Turns her head back towards Dragon!Rainbow and roars in rage] "You weakling! You dare to slap me!"
[Spreading her own wings, the dragon queen charges forwards, claws ready to grab Rainbow, but this time she is ready, she leans back and grabs Dragon!Chrysalis and uses her own momentum to throw the Queen over and past her. She hits the ground face first with a satisfying sound, grinds to a halt]
Dragon!Rainbow Dash: "You have much to learn about agility and letting your anger getting better of you!" [Smirks and leaps to Dragon!Chrysalis]
[The two behemoths engage each other, kicking up dirt, rocks and trees, the fight soon obscured by the huge dust cloud, with mostly only swinging tails visible, and rest of the mane 6 watching]
Rarity: [Looking the fight in awe] "Oh dear... Twilight, is the anything we can do?"
One could only imagine how much fun Chrysalis is having.
"Foolish flying reptiles - they thought us Changelings as easy prey; has it never occur to them that we can't change into dragons to deal with them ourselves? Quite typical, really.
Now... how should I play with them first?"
--- Queen Chrysalis, in her newly acquired mountain-sized dragon form, after taking down yet another band of dragons raiding her realm. Following some depraved fun with them, she unceremoniously swallowed them all, just as she had previously done with the previous dragon raiders, an invading Griffon army, a few rebelling Changeling hives, an entire obscured hedge kingdom of Diamond Dogs, several remote towns and villages in Equestria and Saddle Arabia nopony would miss, among others.
Any of her victims that she didn't devour, burn to ashes, crushed or otherwise destroyed, she took them by the claw-full - sometimes uprooting the entire settlement - took them back to her new mountain lair, where she would toy with them for her own pleasure. She is only prevented from escalating her new reign of dragon terror by the original mountain-sized dragon queen, Tiamat, and the four Alicorn Princesses of Equestria acting as deterrence to her indulgences.
Horrifying, I know. Just imagine what her average day in her new dragon form would be like...
= = =
[With a last, single gulp, the remaining inhabitants of a village was sent screaming down Chrysalis' gullet]
Dragon!Chrysalis: "Oh, yesss... that really hit the spot..." [Rubs her draconic stomach, from which faint sounds and rumbles could be heard] "Yes, squirm! Squirm inside me all you like! Know that more will be coming to join you!" [Burst into maniacal laughter]
General Pincer: [On an airship hovering next to the dragonified queen] "And I fear for us all for that..."
Dragon!Chrysalis: [Swirls massive head to Pincer] "WHAT did you just say?"
General Pincer: [Quickly grabbing for words] "I mean... that is... if you pardon me, your highness, you seem to be enjoying yourself perhaps a little bit too much."
Dragon!Chrysalis: [Rolls draconic eyes] "Well, of COURSE I am! This new form of mine is truly exhilarating! I can see now why those puny Princesses of Equestria loved that spell to bits - vast armies now became nothing but swarms insects to be crushed beneath me, mighty fortress become less than fragile sand castles and ant hills! Whole forests could be burn away in a single breathe, whole cities are just like shrunken models that could be held in my claws, its people... the taste of them, oh yesss..." [Hiccups unroyally] "I never realize how much an elder dragon could eat in one go. I wonder how Tiamat manages..."
General Pincer: [Snarking without subtlety] "Your highness, I fear you had really let yourself go this time. Your majesty should consider slowing down lest you let your majestic new form..."
Dragon!Chrysalis: [Glares at him] "You finish that sentence, my loyal minion, and I should consider you food as well!"
General Pincer: "Of course I mean no offense, your highness! Besides, your majesty already had your fill of your own changelings last month."
Dragon!Chrysalis: "Those hives who rebelled against me are not my Changelings! And I barely had my fill then - had you not persuade me to spare the civilians in those hives, I would eaten them along with the rebels and their leaders in their thousands, just as they deserve!"
General Pincer: [Shudders at the recent memory, realizing his queen now sees her own kind the same as everypony else as a giant dragoness] "Well, I must warn, the international community would not take kindly to that, or what you did to those Griffons, those Dragons, those Diamond Dogs as well. And if they found out you had been secretly devouring or... taking frontier settlements and their population for... personal amusements, I shudder at their response. The Alicorn Princesses still have their dragon forms and are unafraid to use it ..."
Dragon!Chrysalis: [Annoyed] "Pah, since when did I ever care about what they think! They may be able to stop me now if they act, but I am patient - I shall bid my time. One day, I will know how to reduce them back into their pitiful forms, or become even more powerful than they are, and when I do, I shall destroy them and all of Equestria! And then..."
[Dragon!Chrysalis slips into her own daydream - her dragon form, now towers over the clouds and the world, using an entire island as her throne. All her enemies are defeated, especially the Alicorn princesses, and are either doomed to end their days in her belly or as her toys. Her own people, now turned to Changeling Dragons, serves her every whim, offering her entire civilizations of cattle races in the world in their millions - and even offering themselves - to satisfy her ravenous hunger and thirst for pleasure. All the cattles' riches are piled into mountains around and over her. All the world, and perhaps beyond once she figure out how to cross parallel universes, will be part of her hoard, for all time...]
Dragon!Chrysalis: "... Anyway, general! Is there any more remote cattle settlements around this area? I am still feeling a bit peckish."
General Pincer: [Gulps in fear] "The only one left is this pony town called Appleloosa to the north-west, but it's too deep in Equestrian territory. I beg you to reconsider..."
Dragon!Chrysalis: [Snorts] "Your request has been noted. And rejected! A healthy Queen needs her nutritious meals. But if it makes you feel any better, we'll make it a quick stop-over: just snatch up a few of the cattle, stomp a barn or two, then leave. Remind me to NOT eat a few, though--Pupa needs a few new 'dolls'." [Chuckles, almost motherly] "Little grub's so clumsy playing with them; she always steps or sits on some by accident...hehe, might have to try that second one some time! I still can't break that silly habit she has of letting them go once she's bored with them. She's tasted a few like I told her, but she always spits them out! She even apologizes!"
[As Dragon!Chrysalis rambled on about her transformed daughter, General Pincer felt dread engulf him. He knew there'd be no deterring his Queen from this course...]
General Pincer: "Y-Your Majesty... Please, don't go through with this..."
Dragon!Chrysalis: [Ignoring him] "Maybe I should bring her along? It's been a while since I took little Pupa on a 'field trip'..."