Protecting yourself when moving out of an apartment, but staying on the lease?

You could have a contract drawn up between you and your roommate, stating that you are not responsible for any damages etc that occur once you've moved out. You'd have to have proof (preferably, pictures as well as having the landlords do a walkthrough) of the state of the place as of your move out date. In the event that there were any damages, you would be responsible to the landlord according to your lease, but you would have the right to sue your former roommate for your losses. Really, it's a lot of drama. The simplest thing to do would be to find a new roommate to take your place for the remainder of the lease when you move out.