It's easy for a band to turn off a lot of fans if they change their vocalist, but what about instrumental members?

Kaiser Chiefs comes to mind for me; their drummer Nick Hodgson was the main songwriter and after he left,, the songwriting went downhill. Also I don't know what the consensus is in the Coheed & Cambria fanbase, but I feel like they lost a lot of energy after Mic Todd left (although I'm aware of the circumstances regarding his departure).

Edit: Just received the 'concerned Redditor' message... wonder which fanbase I pissed off...