1. If they're looking for something specific they may be able to find it, but analysis is vague enough that I don't feel comfortable just saying yes, blood mages and alchemists can find traces of anything in a sample of blood, even a contaminated sample. But it sounds like they're specifically looking for Starscourge, so sure, they'd be able to find it! though they may not know what they're looking at if they're not from FFXV. (You linked the top level so I'm not sure which characters/threads you're referring to.)
2. Yes. Characters are not actually altered and they did not lose their powers in any way, they're just being converted into Avalon-style magic. Everything is still there, no one took anything away.
3. The scourge being rendered inert would not undo the psychological/mental development he gained from going through his experiences. Per the Wiki:
"Although initially having no interest in revenge, Ardyn's mind began to deteriorate after he started to daemonify others en masse, and being forced to experience his victims' memories is implied to have warped his personality to a husk of his former self."
Ultimately, the damage has already been done regardless of whether the starscourge is inert or not. If Tonake wants to develop him further in-game, it will have to be done the old-fashioned way through character development.
no subject
2. Yes. Characters are not actually altered and they did not lose their powers in any way, they're just being converted into Avalon-style magic. Everything is still there, no one took anything away.
3. The scourge being rendered inert would not undo the psychological/mental development he gained from going through his experiences. Per the Wiki:
"Although initially having no interest in revenge, Ardyn's mind began to deteriorate after he started to daemonify others en masse, and being forced to experience his victims' memories is implied to have warped his personality to a husk of his former self."
Ultimately, the damage has already been done regardless of whether the starscourge is inert or not. If Tonake wants to develop him further in-game, it will have to be done the old-fashioned way through character development.