His actual lines:
...I have lost many things, but my mind is yet my own.
There upon the stage I stood, prepared to take my final bow, only to find that the finale was but an intermission...
Shall I use this chance to repent for my sins? Embrace goodness and mediocrity? Nay, I think not. While the one I yearn to face yet lives, the hunt must go on.
The framing it as a "performance" sounds much more like Zenos's willing death than Asahi's unexpected one. Also I never got any impression from this that Zenos was surprised to be dead, or had only recently come to the realisation.
My interpretation of it is that after "taking his final bow" he expected oblivion and instead found his soul still trapped in his now-dead body, but was later able to 'escape' and take over the unfortunate Resistance soldier, most likely someone tasked with handling the dead in the aftermath of the battle. So he's been lurking around for however long it's been since the liberation.
The question is, does Elidibus know that Zenos still exists, or is he a complete wildcard?
Also - as I've said in earlier discussions - whatever is going to happen with Zenos from here on, it has to be more interesting than simply defeating him again. There must be some kind of plot purpose for it.
I wonder if he might save us from another threat at some point? A "nobody gets to kill you except me" kind of thing.
Also possible that he *has* been doing a bit more soul-searching and feeling some regret for his past, if he feels he has to monologue about how he's not going to repent...