He may have killed the would-be king demon, but chances are pretty high that he would have had people in his shadows pulling his strings, be it the spouse, relatives, advisors, other nobles...etc, who are the real big bad, with the king being a mere figurehead.
Now that he's changed the timeline, I'm curious if he'll still get with Irene, have a harem together with the childhood friend, or get friend-zoned by both.