If the principals are still alive, I can see the Beatles (with John, not Julian - they would never have done that) closing the London show, and Elvis closing the Philadelphia show.
More interesting are the no-shows that could have been there but weren't. Boy George was starting to get into his heroin problems at the time, and that supposedly took out Culture Club. Billy Joel and Huey Lewis had other commitments. The Eurythmics I'm not sure about. Cyndi Lauper was ill, IIRC. Prince begged off but sent a video; Bruce Springsteen was asked but declared his band needed a break after a year of touring. Stevie Wonder was also asked but supposedly said he didn't want to be the "token [n-word]"; puzzling since other performers were black. Michael Jackson I don't know about, but this was after he'd been burned doing that Pepsi commercial.
Oh, one more not-deceased: Marvin Gaye, had he not been shot the year before, would have been awesome at Live Aid.