Assuming there is a large scale rebellion/revolt/civil war, any person willing to turn against the government probably knows that they will lose their pay if they work for it and the death penalty if they lose. As for supplies, again it depends on which parts of the military do revolt, and if any rebel movement can set up manufacturing in controlled areas, then that will be one less problem.
Of course most of this conversation is based on conjecture and debate. And there are examples of militaries turning against their own governments.