User blog comment:B214/High School DxD EX/@comment-111.94.43.65-20150726145323/@comment-3965848-20150726153408

Maybe they'll will disappear after every changes at that point, but as a cause their future will be reset, they'll still exist as if never travel back to begin with.

Or maybe are going through a chrono nexus, like things in the future can only happened by going back in time to cause it, also known as the Bootstrap Paradox.