Hard to tell how long it might live since it had such a rough start. Hopefully he's got another 10-15 yrs in him. I know for koi and goldfish, if they are exposed to poor conditions and severe disease early they rarley reach full growth potential and they just don't live as long. What ever he has left in him tho he'll get TLC from here on.Yay, good choice if I do say so myself
Seriously though, it's a good thing you've done taking care of this fish. I'm happy you are keeping it and giving it a good home for the rest of its life.