If he's territorial, he would probably nip him either way, the first time I saw my gourami nip at one of my snails antenna, I got the fish out, and I put him in a letter keeper until I could get him his own tank. Their antenna will regenerate, but they don't seem to be as long in my opinion, and I've heard that after a while they might not grow back sufficiently. I now have multiple tanks and lots of snails. I recently rescues some snails being kept with cichlids, and the damage was horrible. I've posted pics in a petsmart thread I started that shows the damage that certain fish can do. They stayed in their shells for three full days once I got them home, out of fear, they're now starting to do better. So please think long and hard before deciding to put the two together again. As far as the oxygen treatments, take him out as often as he needs it, but keep him wet. Sometimes when one of mine is under the weather, I give them a green bean or two, straight out of the can, but I wash it first. I really hope this helps, and I hope he continues to improve. Please keep us posted. We would love to hear more from you, and pb's advice is priceless, I would be lost without her posts.
My name is Amy, and I am addicted to apple snails.