Well, beware, I'm not talking about the HOUSE OF X issues.
Everytime a time traveler comes back in time (Bishop, Cable) or even better when he changes the distant past (Legion), creating new timelines (like the Age of Apocalypse one), does it make sense that characters will be born anyway, no matter what?
This is the same problem with the X-Men movies. Wolverine changes the events of 1973, but when he comes back to the future (2023), Rogue, Bobby, Peter and Kitty still exist...