I hope they will try for revenge, cuz then we will see them again, and that time they might be reformed for real(Something like Adagio, Aria and Sonata pretend that they regret what they have done to become friends with the mane six so they can steal their magic secretly from them, but in doing so Sonata and eventually Aria actually become good friends and do tell at the end to Adagio that they do not want to go through with it anymore. Adagio gets furious and refuse to admit that she also wants to be friends with them and use the unstable magic to turn back into a Siren, but since it is unstable she start to go mad from the pain and attack everything, Aria and Sonata then tell Sunset of a secret way to they have to open a connection to Adagios mind with a Siren song, but cannot do it unless the mane six lend their magic to them. They agree and through their song the mane six go through that connection into Adagios chaotic mind and tell her that friendship is not a weakness or something like that and Adagio rage of destruction ends).

Or at least, that is a story I would not mind(and all the movies have the villain turn into some kind of demon or monster so it is part of the movies usual story pattern)