If you could bring back one great artist that has

Assuming they resume at age and performance level at the time they passed, John Lennon no doubt.

Janis Joplin? Really?

Duke Ellington would also be a contender.

Jim Morrison could have been an interesting choice assuming he also cleaned up his act from what it was at the time of his death.

Gotta put a vote in for Buddy Holly also.

I think a lot of people really miss Johnny Cash as well including myself.

One way we might still receive something of the better part of Johnny Cash as artist/conservator of traditional American music would be for Rosanne to record a second installment of "The List".

I don't know if anyone considered him great, but I don't see anybody mentioning his name, Jim Croce.

I've been passing over this thread for while now. At so many different points in my life, I would have picked so many different artists, including most of the above. As of today, right now, I'd bring back: Johann Sebastian Bach.
If he doesn't show up, I reserve the right to change my mind.