For us, its not quite the same with tunes. There are a few which only one person can take the lead; if he's not there, we can't play it. More likely, we will hold back on a particular tune or song, if someone who is particularly fond of it or has a great part in it, is temporarily occupied, ie. in conversation in another part of the pub, getting beer or getting rid of a beer.

Please keep the thoughts and comments coming. Thanks again -- Tom