If wounds appeared all over his body, it was probably not (only) ear mites but skin mites. They are so tiny you can barely see them with the naked eye. They bite tiny wounds into the skin to live inside, which itches and leads to hair loss due to scratching.
You'll have to treat your cat for them, probably by washing him with a special shampoo or by oral medication or both. If you have several pets living with you, you need to treat them all at the same time or the mites that leave your cat will infect the next host they find. Since cats are missing some essential enzymes to break down certain organic compounds, they can be poisoned by things that are harmless to humans, like most essential oils. You should only treat him with medication approved for cats or recommended by your vet and not try any house remedies without being absolutely certain that it's harmless for your cat.
You should also be very cleanly for a while. Vacuum often to remove any mites that leave his body due to the medication and wash any pillow and blanket he was in contact with. If you cannot wash an item, put it into a big plastic bag and throw it into the freezer for 2 weeks to kill any mites.
As for the tail, it might look worse than it actually is, but a vet absolutely needs to treat it. From the picture I cannot tell if the whitish stuff is a scab or a flesh wound.
All in all the prognosis for your cat is very good. Mites are a bothersome pest, but as long as he's not weakened by a secondary infection, your cat can recover completely and his hair should regrow within a month or two.