How many classic (and your milage may vary on the term “classic”) 60’s rock bands could still reform today with all their original members? Are there any still going with all the originals? Buffalo Springfield/Crosby Stills Nash Young come to mind - and let’s define original members as the one on thier first album or single. Let’s see how many we can come up with!
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The four original Kinks are still alive (Ray & Dave Davies, Mick Avory, Peter Quaife.)
Just missing the 60s (first album in 1970): ZZ Top.
The Moody Blues (Both the Denny Laine and Justin Hayward versions)
Buffalo Springfield is out, then: Bruce Palmer is deceased.
Cream just reunited all the original members this very week for a run of shows at the Royal Albert Hall.
Well, as far as I know, Ian McDonald, Robert Fripp, Mike Giles, Pete Sinfield and Greg Lake are all still alive, so the original King Crimson could reunite.
I was just about to mention King Crimson; also Yes and Jethro Tull. All three bands still exist with just one or two founding members, but all the originals are still kicking.
Brewer and Shipley (“One Toke Over the Line”). Their first album came out in 1968; Jim Messina was the only additional musician. B&S seem to be still performing together after reuniting.
Buffalo Springfield may not make the list, but it appears their spin-off group, Poco could reunite with all members.
Pink Floyd’s original members are still around, but unlikely to reunite.
I was popping in here to say just that: my favorite saying about it is that there is a better chance of all the original Beatles reuniting than all of the original Floyd.
You think that would be hard? Try reuniting the short-lived transitional lineup that had Syd, Roger, and Dave Gilmour at the same time.
Don’t forget the horn section! 
The members of The Jeff Beck Group are still alive and kicking.
How about Genesis?
All appear to be alive (note: Phil Collins & Steve Hackett joined in 1970).
I nominate The Move (predecessor to ELO) could reunite.
I think the original lineup of Jefferson Airplane is still kicking.
Skip Spence died in 1999 but Signe Anderson and the rest are still alive AFAIK.
And Cream’s follow-up, Blind Faith, would also qualify. I think Trafficwould too.
I knew Biffy wold beat me to King Crimson.
Sadly, there will be no TRAFFIC reunion. Chris Wood has been gone for several years and Jim Capaldi died last year.
Also, I seem to remember that all the original members of Santana were on stage a couple of years ago at their Hall Of Fame induction.
Nope. Ric Grech is gone.
Well, the Monkees may not have been an authentic band, but Dolenz, Tork, Jones & Nesmith are all still alive.
Peter Yarrow, Paul Stookey and Mary Travers aren’t really a “rock” group, I suppose, but they’re still alive and still touring together.
I think all of the (Young) Rascals are still alive, but Felix Cavaliere isn’t talking to anyone else in the group, so a reunion is unlikely.