I suppose that completely destroyed cartridge bearings could stop you in the middle of a ride. I've never seen this, though. I think they get obviously gritty and noisy, with obvious drag, way before that happens.

The rear hub has 2 bearings for the bike weight on the hub (in green here), and two or three bearings on the removable hub shell (in blue) where the cassette is mounted. This takes the pedaling force from the chain. These have smaller balls to fit within the hub shell.

For example, from https://singletrackworld.com/forum/b...-superstar-v6/