I don't know the idea behind reality warping powers seem to be the bility to alter the present thus as making someone not exist is as simple as not making them exist at the moment.
I understand some people are trying to say but they would make them never exist even in the begining which is not true and I'll use the X-man Bishop for this little demo.
Bishop comes back and helps stop something bad from happening after doing said deed he still exists even after time has been altered. Now this means that while reality from that point on had changed he still existed in time because he was outside of the reality that had happened by being out of that reality and in a different time.