my v reg daewoo passed its MOT yesterday - woohoo. My rear view mirror fell of ages ago and a couple of attempts to resecure it have failed - I therefore have left it off. When it falls of it switches on my hazards and drains the battery, anyway point is, you do not need to have one to pass the MOT - I got an advisory for that and for the rear wiper not having a blade on it - wasn't that bothered as I can't see out of the rear window as i haven't got a rear view mirror.
Anyway, it is surprising what you don't need to have for an MOT - so good luck!