With proper stage lighting you should be able to stop down further, unless you're going for a shallow depth of field look. If so, there's nothing wrong with snapping a few shots in quick succession and hope at least one of them is in focus.
Ido this quite often for the reason you described. Put on the motor drive, AF-C and do some short controlled bursts of 3-4 images at a time. Yes, you gotta go through more images at the end of the day, but your potential for getting an in focus shot increases. At least that has been my experience.