User blog comment:Kogath/Monster Hunter: World Discussion/@comment-25083735-20190604201317/@comment-26421638-20190605084116

While Fatalis return may be possible (at this point is really likely, maybe as a post-release monster) I don't think that will be the new final boss, so far final bosses had always been new monsters. At this point I'd expect something new, not even related with Xeno'Jiiva.

Former final bosses like the already mentioned Fatalis, Akantor, Ukanlos, Amatsu or Alatreon may return, but I'm 99,887% sure that (if they will return), won't be related with main storyline and just pure Endgame content.