The big question would be what actually happened to either A) stop him, or B) make him decide to fake his death and vanish for a decade.

Evil overlord list rule 230 is "I will not procrastinate regarding any ritual granting immortality.". Which he's shown to be aware of.

It makes sense, remaining evil overlord allows him access to all the materials of dark rituals and willing assistants, once he's achieved it successfully he has all the time he would like to do anything else.