Queen and Paul Rodgers, Faces and Mick Hucknall, ... It depends a bit. I saw The Who with Pino and Zak and they still had the two main singers. I liked that gig, although I would give my left ear to see them with Moon and Entwistle.
With my band we always joke about it. In twenty years our lead singer will sing our only hit and some cover songs on the back of a truck om fairs, with music on tape and all tuned down a bit so he can reach the high vocal parts. He will be The La La Lies. At the same moment I will play with a lot of young guys, myself playing bass seated on a chair as The Original La La Lies. All happens, while our guitarist still makes records as The Real La La Lies. And the drummer will be dead of course.