Many years ago I broke my wrist (yeah, yeah, morris leapfrog after too much cognac). My singing partner and I sing many 2-part a capella songs, but when we accompany I play the instruments. We had a number of gigs coming up. We offered everyone the opportunity to cancel - a few did. Most said, come along and do it anyway. We did, had a great time, so did the audiences. Nobody complained about not getting their money's worth.

Another time I had laryngitis, and was forbidden to speak. My partner does most of the lead singing, I generally do the harmony. I played the instruments and sat there. Communication was fun. The audience was mostly in hysterics. Again nobody complained.

And another time my partner was in hospital. Rather than a solo show (which I have offered in similar circumstances, again giving the organizer the option to cancel), I brought an available friend, a recognized performer, as my "partner," and we alternated songs, accompanying and singing with each other when it was appropriate. Of course I cleared this with the organizer. The audience had a great time.

You do what you've gotta do, and folk music should be flexible enough to adapt. If you really can't perform, cancel. But especially in the States, where "coffeehouse" concert series usually do one a month and book the whole year in advance, it's not easy to reschedule. Villan and Breezy would probably have cancelled me, but they would have missed something different. It's not necessarily the performer's job to reproduce his recordings.