Found this on WIKIPEDIA, though I must take it with a grain of salt.
"Harrison first asked his fellow Beatles to appear. John Lennon agreed to take part in the concert, however Harrison stipulated that Lennon's wife Yoko Ono not perform with him. Lennon agreed, but left New York two days before the event following an argument with Ono regarding his and Harrison's agreement that she not participate.[citations needed] Paul McCartney declined because of the bad feelings caused by The Beatles' legal problems on their break-up. Ringo Starr, however, readily agreed to appear."
Don't really know if thats true or not, but would it have led to something more, or just a one time gig?
The Wiki article is from "The Concert For Bangladesh" entry. I adore that concert, and it would have been even greater to witness a Beatle reunion, but I guess that it just a pipe dream. Though Billy & Eric & Klaaus are present...

I think that that's basically true, or at least it agrees with what I've heard over the years.  My take on McCartney was that he wanted to talk business (about the dissolution of the partnership) and if Harrison did, then Paul would show up.

I can't imagine that it would have led to a reunion.  Except for McCartney, they were all at the peak of their solo popularity, so it wasn't like they needed to get together again.  Besides, Harrison was probably still enjoying his "freedom" from the band, so he wouldn't have been in any hurry to re-form the Beatles.

Quite so, George from ATMP to Bangladesh seems to be his peak for me.
Paul too with RAM, its sorta their post break up creativity coming thru. Getting back together at the time wouldn't have been the best move. At least until they all run out of ideas?

Quoted from Mellotroniac

I adore that concert, and it would have been even greater to witness a Beatle reunion, but I guess that it just a pipe dream.

Me, too. Great concert. There are various reports as to why John didn't agree to show, but I think it's beyond question that George asked him. I doubt he would have asked Paul, as the sue-me-sue-you blues were too painful at the time.

I read this huge Keith Badman book "The Beatles After the Breakup 1970-2000", and you'd find one Beatle ready to reunite, or maybe two, but never all of them. It's the classic herding cats. So I think they all considered the idea at one time, but never could get everyone to agree at once.