I left rats in the tanks overnight and wake up needing to get rid of the smell immediately, I can't imagine after four days... that is nasty. I suffer from "too nice syndrome", I would also have a hard time confronting this issue. I would probably offer to take some of the responsibility, although it might not be ideal if you move out 'cause then the snake goes back to those conditions without the guy being any more educated on the issue. Really, he might just not know how to take care of it. You say he rarely gets on the internet- I would know so much less than I do without the help of this website. Like what I learned from the pet store . Yipes.
Does he ever handle his snake or show any interest in it at all?