I doubt that she would wink out of existence since we've seen other characters cross timelines and universes.
The Tasha Yar that was on Romulus was from the alternate timeline/universe we saw in YE. There is no doubt about this.
Her situation is pretty much the same as Spock's in Star Trek and Into Darkness.
I thought it was now generally accepted that the Abramsverse
exists in a parallel timeline, rather than totally erasing 150 years of Trek history. I'm sure I remember an interview where the writers of ST'09 confirmed this was their intention.
I certainly have no problem with Trek characters popping across alternate universes, since their universe of origin is still intact and carries on without them.
As for other Trek characters traveling back in time along their own timeline
and changing the past to invalidate their own existence and surviving
- are there any other examples? I'll need to do a little research I think!