I don't see it, not in it's current form anyway.
A game like GTA needs to be able to poke fun at everything and everyone. I don't see that lasting much longer.
GTA will continue to exist for a long time sure, but not in the form that made it so great in the first place.
I think it will focus more on going up against very clearly defined "bad" guys and it'll lose a lot of the humor and indiscriminate violence. I think it was Watch Dogs 2 where aim assist didn't even work on civilians? I think it's going to be that but amped up over time (maybe one day you'll only be able to shoot criminals or something).