If gangrene is not yet present it certainly may set in and when it does.. Without antibiotics its fatal to these guys. In many cases the blood supply to the tail is damaged, causing death to that section back. Sometimes it will become brittle and break off on its own, other times then well.. Do as I suggested above. With gangrene they can look perfectly fine up until their death - It hits real fast in reptiles.
If amputation occurs something like sudocreme (an antiseptic) or silvadene cream (commonly used on burn victims and works great for this purpose as well). Regular old neosporin is effective when you cannot find the higher grade meds. When it comes to the tail wound ideally you actually want that wound to heal naturally open air - it does not look the best and it grosses people out... But if kept clean it will heal better this way. Just make sure the area he lives in is super clean. I am not sure if you've seen a regrowing tail, the end of it will cap off into a sort of very strange grayish looking cap and will eventually start pushing gradually when the tail begins to regrow.
I think I need to start watching my grammar skills.