In reply to LastBoyScout:
> Depends on how car-savvy the owner is - it might pop back on and you'll be fine.
> If it is damaged and needs replacing, then it gets expensive due to the complexity of modern mirrors - remote adjustment, heated glass and, especially, colour-coordinated trim panels will need painting (unless they can be swapped over). Problem is that it will probably come as a complete unit.
> If it was my old car when I had time, I'd get a replacement from a breakers and swap them over. On my new car, I'd probably want a new one fitted - partly because I don't currently have the time to source the part from a breakers and take the door apart to fit it.
Indeed. I had by mirror broken whilst it was parked. Unfortunately no note left by an honourable person like the OP, so I had to deal with it myself. My first port of call was my local garage. They said the full price for a new replacement including fitting and VAT was just under £450. Once I had recovered from the shock, they suggested the breakers yard route, and located one although it was the wrong colour, which they were happy to respray. Total cost £150.
Quite frankly it looked as good as new, and there was no way of telling (at least to my lay eyes) that it wasn't new.
So, to the OP, if a total replacement is required try and persuade the owner to recognise your honesty and go down the breakers yard route even if that means a respray. Good luck!