It only makes sense that if you stop to eat/pee/drink, whatever, that the people behind you either:

a) choose to stop to eat/pee/drink, whatever

or

b) tee off


Normally if they're playing through, they'll leave their bags by the tee while they duck in to relieve themselves quickly, or they'll leave someone on the tee as a placeholder.

But if a foursome disappears, and there's no bags on the tee, I play.