The definitive rock n' roll replacement rule?

Here is what I've come up with after out lengthy comment discussions under The Cars reuniting post.
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Rock n' Roll Replacement Rule:

A great lead singer and/or great lead guitar player can ONLY be replaced with another fairly large star unless the singer/guitar player leaves the band because of their own personal DEATH. Everyone else in the band is expendable. However, you cannot replace BOTH the lead singer and lead guitarist in any way, shape or form unless you are Deep Purple.
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I think that's pretty good.

Deep Purple is the exception because they've replaced everyone in their band 206 times. I played with them in '86 and I was only 9 years-old and it was for only 3 shows in Mexico. During Live 8 the DJs on XM radio were literally playing a guessing game to see who could figure out who was going to take the stage when Purple went on in Canada.

You can replace drummers and bass players and rock on. (See: The Who, Metallica)

AC/DC replaced a great singer with an unknown, but through death and rocked on.

Lynyrd Skynyrd is living proof of the rule. A plane crash killed the lead singer and lead guitarist. They picked up the singer's brother (with a nearly identical voice) and since they were running a 3 guitar attack anyway, one of the other guys became lead. Another guitarist died later and ultimately they brought in Ricky Medlock from the southern rock band Blackfoot who had some big songs on its own. Granted Skynyrd isn't as big as they were in the 70s, but neither is southern rock in general.

Van Halen replaced David Lee Roth with Sammy Hagar who was a big star on his own and despite my views on the VH3 album, flopped with Gary Sharone who wasn't a big enough star to replace DLR or Hagar.

Guns N Roses is a non issue really because Axl will never do anything on a regular basis, like create new music or tour. So we don't know if he can pull off GNR without Slash.

So what do you think? I think it works pretty well.