@ZeroWWE I doubt that they would actually capture him just to experiment on the imp. Because if they really wanted to do that there's already thousands of monsters literally everywhere that they could do that with. But so far he seems to be the only one who can be reasoned with and I think they would at least attempt keep him for information and also potentially for negotiating with the other side if that's possible.
well, we know that eventually, human and demons came to an understanding.
assuming imps lifespan is somewhat close to a human, it's very likely he was one of them who made it happened unless he was executed/experimented on.
Hopefully, we might find out in the future.