So you know, SMF can actually have file-based sessions as well as db based sessions, not sure which would be more adviseable for you guys though. I've actually suffered from the sessions table crashing as well, but only thrice in MT2's entire history, and not once when moving to the 2.0 line starting with the Alphas.

The call on which method to deal with sessions is up to you. But do upgrade ASAP. (my offer to do it for you still stands)