In my humble opinion, trying to glue the fin back on is just about pointless. It won't stay on, and you don't need it, so why bother?
I do think that you should check the fit of the screws. If you broke the head fin installing the new screws, then chances are that the reason it happened is because the heads of the new screws are a bit big, and are not seating on the flat part of the pocket in the head. If this is the case, then you need to grind the seating surface of the screws down a bit to match -- otherwise it'll just be perpetually loose screws, more broken fins, and possibly a warped head.