Nice story here about Michael DelGuidice, a musician who went from being in a Billy Joel tribute band to being hired by Joel to play in his band and help him out with the vocals.
The best tribute bands are better than the bands they're based on because they work harder at it and as soon as one member can't do the job they replace him.
The best backing singers are better than the singers they back because they're younger.
A few years back I saw the bus carrying "The Glenn Miller Orchestra". Obviously none of the original musicians and clearly no Glenn. They're licensed by Glenn Miller Productions. They keep the sound alive and cater for the audience that wants to hear that sound.
Maybe Billy Joel Productions will be doing the same thing in the future.