Depend on the band. I was telling Matt exactly my viewpoint about some bands in another thread
http://www.ultimatemetal.com/forum/old-school/531356-black-gives-way-blue.html#post8588441.
I can agree with him and others than Judas Priest without Halford is not the same. But consider this:
a) Owens is a great vocalist but he suffered from bad composition from Tipton, what would have be if the composition had been like in "Painkiller"?
b) Halford is back and look at his performance live, not to mention "Nostradamus"
Iron Maiden is linked ultimatately to Dickinson but:
a) I can't imagine the first two albums without DiAnno
b) The band was already loosing force by NPFTD
c) Blaze was indeed a bad choice (sorry JD), but Dickinson returns didn't improve much IMO.
Queen or Thin Lizzy are a good examples of bands that can't work without the lifetime lead singer. Tank is another, I think that upon Ward retirement they should have been disbanded. And of course who will think that Motorhead can be Motorhead without Lemmy? (no Rob, you are not allowed to comment on this
).
Candlemass on the other hand is a band that has benefited from changing from Marcolin to Lowe. And the band was just coming from a reunion with Marcolin with a damn good album and their popularity was rising. Even so, they let Marcolin go, call Lowe and the last two albums has been brilliant.
A lot of VH fans accepted Hagar instead of Roth, except for the sincgle case you mentioned in another thread Arch Enemy fans like the same or more Gossow era than Liiva. Marillion have more albums with Hogarth than with Fish and I think that means a lot of fans accepted the change.
I prefer both Sentenced and Amorphis with the clean vocalist, so the change for me was for the best (regardless of what happened afterward with the band). And let's not forget AC/DC, they survived damn well the demise of Scott and the coming of Johnson.
I think the band that changes or lost the lead singer suffers the most if:
a) the vocalist is one or the main composer
b) the charisma on stage is such that the replacement can't compete
c) the vocalist owns the band
And the final thought...the eternal hate/love discussion in the forums: James LaBrie. Will Dream Theater be the same if he's gone?