You can restore one dead musician to life. Who would it be?
So asketh Fightin' Steve H. Answers range from classical (plenty of Mozarts) to the more contemporary (at least one ODB). But the question itself asks more than it seems to. Professor Horwitz's own answer (John Entwistle) illustrates something about the nature of production in what is basically an extension of folk music.
The sole reason to bring back a Mozart or a Liszt or (my own pick) a Dvořák (okay, you caught me—I'd actually choose Grieg) is because they'd have a few good compositions left in them. Beethoven could have easily produced more work on par with Für Elise; Mozart could have had another Requiem in D minor or two given a few extra years on earth; Russian ballet would have certainly benefited from an extra Tchaikovsky composition or two.
But folk music, including jazz, blues, rock and roll, and their many offshoots combines the songwriter with the performer. In a way, most of today's pop where the performer doesn't get within arm's reach of a pen and paper hearkens back to the days of chamber music. But for much of the 20th century, the person on stage is the person who wrote the song (for the most part). Bob Dylan is Bob Dylan as much for his nosebeast yawrl as for the contents of his lyrics.
So if you were to bring back Entwistle, it would be for up to two reasons: 1) you expect he'd produce more studio work and 2) you want to enjoy a live performance. The second reason is inapplicable for a Handel or a Strauss. In other words, the marginal revenue product of a singer-songwriter is separable into two parts: the composition and the performance. If you lose one person, ceteris paribus, you lose two sources of value generation. The BATNA disparity for keeping a singer-songwriter alive is higher than for keeping a composer or a performer alone alive.
The recent trend towards separating these two functions therefore makes today's pop music more euvoluntary than in Janis Joplin's time. Right? Specialization of trade is limited by the extent of the market, yes? Cheap digital distribution means that the slog of studio production can be sourced to specialists, while the pretty people with questionable chops can run the tour circuit. Isn't that how it's supposed to work? The Wal-Mart model reigns supreme?
To answer the question however, I'd bring back Dwayne Goettel. In a flash.