Wow, I'm really sorry to hear all that.
Personally, I'm not sure what will happen once his nose-rub heals over, but w/out seeing it, I can only wager it improbable... Perhaps another user can offer more concrete feedback.
As to the open-mouth "hissing," sounds like he may have another RI. Is there a lump in the throat, or to feel it, do you feel any swelling?
As to the rest, put him on newspaper if you've not already (will keep dust and debris from the healing wounds and decrease irritation with his already labored breathing), keep your temperatures steady and provide as much comfort (a hide on either end of the enclosure and outside a high traffic area) as possible.
A vet-inspection would also be wise, just to get another opinion if nothing else.
