answer:Firstly, as far as permission, the owner of the property, or landlord is the one you would get to say “yes or no”. I think in this scenario, your roommate needs to take full responsibility for all the efforts involving the sub-leasing of the room. If he’s the one that left, and he doesn’t want to come back, and he doesn’t want to pay the rent for his portion in his absence, then yes he should certainly bear the entirety of the burden for the sub-lease. He’s gotta pull his weight somehow, he should have no excuse for putting that on you. And for a direct answer to your question, sure it’s “OK” to say no to your roommate, although I’m not sure why you would say no to him wanting to sublease it. It sounds like you want to say “no” to doing all the work for him. But it seems like you dont have much of a choice either way.