#1 and #2 apply, unless the snake is ill and you rack up a large unexpected vet bill, or worse, the illness spreads to your other snakes.

If you're practicing strict quarentine, and the snake plumps up and is healthy(despite his ill treatment) then the snake and you are better off. No bad keeping for the snake, and no wondering if the snake is being cared for for you. Good on both ends.

Ball Pythons are remarkably hardy and 3 months isn't such a long time that I'd be particularly worried. The lack of heat would worry me more. If you read the threads on here you'll see snakes that have gone on voluntary hunger strikes for longer than 3 months with little to no ill effect. I'm sure he'll do well with his new CARING RESPONSIBLE owner and you should have no issues placing him into a good home if you chose not to keep him forever.