You can dismiss him after you complete the quest.

Make sure you keep your sanity above 0 or else a catastrophic event gets triggered (ie. a cannibal eats people). What event gets triggered is random but depends on how much sanity (if any) is left as well as what traits your team has. It's always good to carry stuff that replenish sanity - most of them have negative effects, for example: alcohol may make someone an alcoholic, coca leaves may make someone insane and mangos, while safe to eat, will spoil after a few days so if you don't eat them by then it'll be a waste of resources. You'll figure out what's best. ;)

Take him to a Shaman or feed him a green mushroom. You will get much nicer reception back in London and you won't have to worry about him eating someone.

Actually, if you keep your sanity up and rest in safe places, he should not be a problem. I like having him along for the extra die and crate.

I've had him cannibalize people even after curing him. My advice would be to either map out and explore everything before rescuing him (just don't explore the camp-site) then do a quick sprint with high sanity to the end point, or to just deny the quest from the get-go since $100 is hardly worth an end-game companion.