I won't advocate for theft but hopefully they will try to improve or realize how badly they have done they will see no other option but to give the poor snake up for it's own sake.
It's very possible he has an RI after being in the cool basement for so long and being so weak and thin, his immune system is probably shot.
100 degree warm spot is way too hot for a corn. I keep mine at room temp in my snake room (75-85ish).
Corn snakes are very hardy but it's still possible he may die from wasting so far even with proper care at this point, just want to mention that in case he does pass.