Time is a funny thing in science fiction. How it behaves depends entirely on the author or scriptwriter and how they want time to behave within the context of their own stories.
Look at the new Abrams timeline in the Trek franchise. In the Roddenberry and B&B eras a radically altered timeline would have been repaired by either our heroes to set things right or by time-traveling "temporal cops" from the future who monitor the flow of history to make sure nobody's screwing with things. It might have taken a two- or three-part episode to correct things and return the known universe to the way it was, but it was done and our heroes went back to the bridges of their starships or space station and relaxed.
Now we have what appears to be a permanent or at least semi-permanent new temporal events sequence that takes place parallel to the Prime/original timeline of Trek and one - it appears - no Federation timeship from the 29th, 30th or 31st century is in any rush to correct.