What happens when they run down?
They stop. No?
Of course they stop. (I'm stupid, but not that stupid!)
Do they stay together as they run down or does the synch. come apart?
Oh dear, oh dear, oh dear!
Well, we've now gone from physics to clockmaking. It would depend on the escapement energy in the clock mechanism in relation to inertia/mass. That is, the mechanical energy stored within the spring to be released in a repetitive sequence. The synchronis movement would continue until the springs/escapement could no longer affect the "whole." Once you have less than 50% of the metronomes in action, they would start to go out of synch as they would no longer contain sufficient stored energy to affect the "dead weight" of the stopped ones through the movement of the base.