Personally, I think your angels probably would have been fine in your setup as long as the banded leporinus was moved. They're known to be nippy so he was probably the culprit. Moving the angels works, too.
By tail, do you mean just half of the fin was missing, or was actual flesh eaten off of the fish? If it's just the tail that's damaged, as long as the fish is in a healthy tank with good water parameters the fin should heal up without a problem. If the fish had more severe damage, he should really be in a hospital tank and be treated with antibiotics to prevent infection.