system
Given the following post, respond as if you're commenting on Reddit:
human
[Avengers: Endgame] what if Nebula didn’t do that?

Go back to 2014 Morag. Isn’t that the whole reason Thanos gets involved? What could possibly happen, according to the “1 in 14million” logic, that would make the heroes lose even if Nebula doesn’t go back to 2014 Morag?
gpt
Any scenario involving Nebula going back in time brings pastThanos to the main timeline, it just matters when and how. Nebula's digitally backed up memory is what attracted Thanos' attention initially, it conflicted since there were two Nebulas. 

To answer your actual question, if Nebula goes after any of the other stones, then Thanos comes for her when she arrives, just as he did on Morag. The difference is that if she goes after the space, time, or mind stones, than Thanos comes to Earth. If she goes after the reality stone, Thanos comes to Asgard. If she goes to the soul stone, than Thanos knows where the soul stone is. 

There's also the possibility that only the specific teams that went to retrieve the stones were capable of doing so, which seems likely, given how events played out.