I have had Sonar blow its driver brains out before too, and I just do a reboot and all comes back like nothing ever happened.
I do this whenever that message pops up like it wants to give me the silent treatment (silent Master Buss).
The most recent loss of Sonar consciousness was Sunday night, when I happened to be recording something when my weekly backup kicked off. It REALLY did not like that.
But, since it was late and nothing got messed up, I just called it a day and got a good night's rest.
Bob Bone