How many pictures to (pick from) to document an average wedding?

A friend is going to shoot a wedding for his buddy and asked me (an
experienced photographer, but not weddings) about how many images did I
think he should shoot "to be sure he got everything". He says he doesn't
know when to quit shooting and "start to enjoy myself".

I think he'll do the usual editing of his output to find the "keepers"
and have an album made up, but mostly he wants to put them into a
documentary a'la Ken Burns, put to music. Video to be about 7-10 minutes
long. Probably about 250 images?? (Pre-ceremony, ceremony, "standard"
shots and candids at the reception)

What sort of ratio do you think he should aim for? Shooting digital.

Thanks for your expert opinions.

Bill