i'd even say, what happens to any player in general.
idk how it works in others mmos but i guess you just lose everything when it happens.
To me it'd be cool (idk if it's doable thought) that every player can download an offline version of the game in which you could play all the chars of your account.
This way even if you lose a lot of the interests of the gale as you'd play alone, at least it'd be kind of a nostalgia game where you can see and play your chars forever... i think that to me it's gonna be really hard to just lose everything i've done during these years, so something like this should exist
What some game developers do when they get tired of their game or simply make no or close to no money from it anymore, is that they either sell it to another developer, or they open-source it and release it to the public for people to be able to run private servers etc.
You can always hope that they'll choose one of these options when the game comes to an end. However judging by how little they've shown to care about their players in regards to support and feedback I'm not so sure they would care about this either.