Yep, I'd never let it go that long. Slippage and "no pedal" would be dead give aways. Don't know about your friend, but I've seen folks drive a car into the ground and then try to keep it going.
Has he looked for broken motor mounts? If the engine is torqued too far out of position, he might get some unusual noises. Again, not very probable, but it is possible.
Does it happen only when driving, only when parked, or during both?