First postulate: a band which is named after the lead singer cannot survive said singer's departure. E.g. Pink Floyd, which became a sad mockery of itself after Pink left*.
Second: a band which has only one major songwriter cannot survive the songwriter's departure.
Third: a band of three may be able to stand the drummer's departure, if and only if the drummer was neither the lead singer nor an amazing drummer. For instance, Rush, replacing John Rutsey with Neil Peart immediately before their first big US tour.
Fourth: in larger bands, any part who is neither an amazing player nor the sole lead singer can be replaced. Consider Styx.
Fifth: if the band shares lead singing responsibilities, the usual lead singer can be replaced. Consider Chicago.
Am I missing anything? Other heuristics?
*Yes, I know.
Second: a band which has only one major songwriter cannot survive the songwriter's departure.
Third: a band of three may be able to stand the drummer's departure, if and only if the drummer was neither the lead singer nor an amazing drummer. For instance, Rush, replacing John Rutsey with Neil Peart immediately before their first big US tour.
Fourth: in larger bands, any part who is neither an amazing player nor the sole lead singer can be replaced. Consider Styx.
Fifth: if the band shares lead singing responsibilities, the usual lead singer can be replaced. Consider Chicago.
Am I missing anything? Other heuristics?
*Yes, I know.