Tim the guitarist from the late lamented Whitby band Banoffi had a frantic style, and in spite of using the lightest possible picks he'd snap lots of strings every gig. The other two played on while he got out his pliers and envelopes, and usually he was back in before the end of the tune. On one occasion I saw him replace two strings during one tune set and he was still back strummig in time for the end!

I usually pass the guitar to a volunteer from the audience (about half are usually players themselves) and either do one unaccomanied or on another instrument. Risky but better than loosing the momentum or getting into a frazzle (I have enough trouble talking and tuning at the same time)!