Destiny said that she had 10-11 lives, and ALSO, mentioned that killing her before her powers activated (when she was sick at 13) that it would break the cycle, intimating directly that's WHY she would only have 10-11 lives and not an infinite number. If she dies before she's 13 it's OVER.
They aren't rewriting or undoing anything, as they keep saying over and over, and Jordan White explained very bluntly, as referred to earlier in this thread.
This isn't X-Men's Crisis on Infinite Earth's, rewriting its history by way of futzing with events in continuity and selective erasures, this is X-Men's Empire Strikes Back, recontextualizing the entire past with new information making us look at it through a different lens.