It can regrow... one way or another. If it will not heal with time on its own, you may have to intervene. I know some people will be against this but you can trim the fish's fin behind the damaged area and it will grow back. The king of DIY (Joey) has a video on youtube with details, precautions and steps to take if you decide you need to intervene.
I preformed this procedure on one of my fish who was not healing on its own. I have to cut way back on the dorsal, and about half way on the caudal fin, and sure it enough it started regrowing. With in a few months it was back to normal.