As groups’ vocalists often seem to be the head of the outfit, what ones have declined when other members have died or left?
The one I can think of is The Allman Brothers Band after Duanne Allman died.
Anyone else come up with anything?
Led Zeppelin, when drummer John Bonham died.
Revtim beat me to Zep.
Not sure what you mean by “declined” but I thought ‘Eat A Peach’ and ‘Brothers And Sisters’ were great albums.
I’d say The Police post Sting. And what was Phil Collins’ band?
Mods?
Another contribution might be The Who, post Moon?
Lynard Skynard?
Chicago, post-Terry Kath. Actually, I just finished listening to them!
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Yup, Cafe Society it is.
No problem. I’ll move it for you.
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Metallica suffered when bassist Cliff Burton died. They put out a good album in …And Justice for All afterward, excepting that it remains noticably lacking in the bass guitar area. Then came a string of albums that each progressively came closer to total suckitude. Then Cliff’s replacement, Jason Newsted, left and they’ve been circling the drain ever since.
The problem with your scenario, however, is that Metallica didn’t get good until Newstead joined the band.
Hmm, after Keith Richard(s) died, The Rolling Stones… 
Actually, Ronnie Vanzant was Skynyrd’s singer; he died in the 1977 plane crash that also killed two other members. However, Ronnie’s younger brother became Skynyrd’s singer during the 1990s.
IMO, The Who’s music certainly declined in quality after Keith Moon died.
I’ll admit that that is a perfectly viable opinion, but that’s not one I can say I’ve ever heard before or agree with. Master of Puppets remains their pinnacle, but that debate is for another thread.
Well it’s a Canadian band and it’s probably open to debate but I thought Blue Rodeo went to absolute shit after keyboardist Bob Wiseman left. They went from being a cool alt-country band to being a sort of boring pretend country adult contemporary band. He’s interesting and the rest of them are not. At least not to me. I just never thought that was any kind of coincidence. He left and I lost interest. On the other hand, maybe he just lost interest a bit ahead of me, him being on the inside and all.
To continue this hijack briefly, allow me to clarify:
Master of Puppets WAS a good album. But I felt like they hit their stride with Jason Newstead. However, the last good song they recorded was, “Until It Sleeps,” and the window has shut.
I hate to say it, but R.E.M. took a nose-dive after Bill Berry (the drummer) left.
Duran Duran started downhill after Andy Taylor and Roger Taylor left. The decline went further when John Taylor left the band with just Simon LeBon, Nick Rhodes, and Warren Cuccurullo.
Weezer began their inexorable downward slide the moment Matt Sharp, the bassist on the *Blue Album *and on Pinkerton, left. Their latest album is one of the worst I’ve ever heard.
A damned shame, too, since those first two albums didn’t have a single weak track on them, just one brilliant pop tune after another.
Wham? 
The band Queensryche really started to diminish in quality when guitarist Chris DeGarmo left.
Didn’t Genesis decline when Mike Rutherford left?
Then why hasn’t Apocalyptica covered a song from anything after Justice?
Because they got YOUR address instead of mine when asking for ideas.