What kind of accident? How'd he lose the leg?
Loki was allowed outdoors whenever he wanted (in the town I lived in there are no leash restrictions for cats, only dogs), and would never be out past dark. One evening he didn't come home. Late the next day, he was just barely able to jump over the fence in the backyard, and was clearly injured. The following morning we took him to the vet (which was a few towns over), who informed us that Loki must have been hit by a car.
His leg was practically shattered. We were told we could get it amputated, or see if a cast could set it. If we went with the cast option (which was more expensive), we would need to keep him very confined and inactive for
months, or else it would have to be amputated anyway. Loki was barely a year old at the time (this was in 2012), and was very active, playful, and loved jumping around, so keeping him confined in a small box for so long seemed completely cruel. So we decided to go with the amputation because it would be easier, Loki wouldn't need to be restrained all the time (just careful of the stitches for a couple of weeks), and since he was still young he could probably quickly learn to get around fine on 3 legs.
We definitely went with the right option. He was completely fine, and has no mobility problems. He has a huge limp when he walks slow or wants treats, and likes to lean on you for support at inopportune times (like, when you're walking haha), but when he runs, you wouldn't know he was missing a leg at all.