[mehrkat]

If you want to avoid killing give him a regeneration/regrowth magic item or wish to give him the advantages. Slow 1 hp / 1 hour or so it means if he can limp away or crawl away or heck even stay still long enough he'll get better and you can throw some battles you wouldn't under normal circumstances because you don't have to avoid killing him. It keeps the game from turning into a campaign of attrition.

I often use it for my oft foolish 12 year old child in games.