Let me start of by saying this: for the way Vi's ultimate is presented, it is supposed to be this un-counterable attack that singles out an enemy for your team to destroy, but there are several ways to escape from it.
The first way, is Kassadin's Void step. If you void step away when Vi takes you into the air, you can escape unscathed. It may be possible to do this with flash, shunpo and maybe even kha'zix's jump-thing.
The second way isn't really a way to escape from it but; you can use Darius's ult during the throw part of Vi's ultimate and land it before her ult finishes.