Former Rolling Stones bassist Bill Wyman left The Rolling Stones back in 1993 and he has gone on record saying Mick Jagger, Keith Richards and the late Charlie Watts could never be replaced like he was.
Wyman went on to talk about how irreplaceable Charlie Watts is:
"You could replace [guitarist] Ronnie Wood. You know, you had Mick Taylor before, you had Brian Jones. But, if Mick leaves there's no band. If Keith leaves there's no real band, is there? You know, and they believe that Charlie the same 'cause I don't think there's a drummer that could replace Charlie. And he said it. He said, 'I'd love not to do it anymore and retire, but I don't want to let the boys down,' 'cause he knows if he leaves the band will end."
The late Charlie Watts did believe The Rolling Stones would be fine if he wasn’t with them. Charlie once said, "If Mick or Keith said that [they were retiring] I think we would [fold the band]. If any of the others said [that], no. I think they could get another drummer, I think they could get another guitar player. But, I think that Mick and Keith would or could carry on. But I think if Mick said I'm retiring I don't know how we'd do a show without him and without Keith."
Watts also discussed the only way he believed any member would really leave the band:
"We never retired. People have left or people have died, but that's the only way we're gonna get out."
[Source: Classic Hits Today]