Is it OK to say 'no' to my roommate who wants to sublease his room?

My roommate and I get along very well. He has been gone for over two months now, and did not anticipate that a job elsewhere would take him away for so long. Now, knowing that he will most likely be out there another month, he has asked that I sublease his room.

On one hand, I understand where he is coming from and totally empathize. On the other, it would be me that would have to do all the work to find one, and, most importantly/affecting, live with a complete stranger who would exist within feet of my most dearly possessions…