What follow-up treatments would he need (let's say if he were a pet and could have everything he needs)? If he will be medically OK without any further intervention, I say release him. I know everyone would love to see him become the next Kurby, but not all cats are tamable. Depends on his age.

If you think he is tamable, CAGE him. (I am certain you have a cage somewhere)

But don't feeel bad if you feel the need to release him. We can't save them ALL and you gave him what he needs to survive.