Saying 'irreplaceable' is conjecture, isn't it? Yes without Steve Howe can still be Yes but a different kind of Yes. I do like Trevor Rabin but Steve Howe's barbs at him from the Union tour are always funny. 'He's playing where there should be no playing!'

Triumph without Rik Emmett is another example. Phil X is no Rik Emmett so Triumph's last studio album didn't really sound like Triumph aside of Gil Moore singing on every track.

It can be argued a Def Leppard with Clark & Willis was a different band with Clark & Collen and then Collen & Campbell. I cannot even fathom what Steve Clark would have thought of X or Sparkle Lounge.