Hmmm.

Peter Frampton would physically cease to exist without Alive!

U2 would be stars but not mega mega superstars sans The Joshua Tree.

Without the help of John Travolta, the Bee Gees would have remained 60s has beens like Donovan. The Saturday Night Fever soundtrack was THE soundtrack of the late 70s.

Radiohead with a big gaping hole where OK Computer used to be would be interesting. Before that, they were Brit pop second rans with a few good tunes. Afterwards, an experimental hipster band that got raves from the critics but made music that was too obscurantist and inaccessible for the general public, despite the hordes of rabid fanboys.