Which Band Member Can You Least Do Without?

I was watching highlights of Download Festival 2011 and saw an interview with Thin Lizzy. They have a new lead singer and that got me thinking. Styx is out touring with a new lead singer, Axl Rose has replaced his entire band, but still tours as Guns n' Roses. Different bands throughout time have had to replace a member due to disagreements or tragedy. Just who is the most irreplaceable member of a band? And eliminate the bands that are named after a member. For example, Van Halen's most irreplaceable part is Eddie because it's his name. So with that caveat, who is the most irreplaceable?
For me, it has to be the voice of the band - the lead singer.