His first assignment would be to unwrite the last Hitchhiker’s book. Then he could do whatever he wanted. (If I can raise the dead, he should be able to unwrite a book.)
My own choice would be Mark Twain, not to finish anything from the last century or two but to see what he could do with this one.
'TERRY."
“Y-y-yes?”
'YOU GOT SOME FACTS WRONG. YOU NEED TO CORRECT THEM."
If you refer back to Hilda’s theory as explained in TNOTB and TCWWTW, you’ll find that’s exactly what he IS doing. :eek:
I’m tempted to say John Kennedy Toole; problem being that a) he might just kill himself again, and b) maybe he just had one really good book in him.
Maybe Ambrose Bierce to write about whatever happened in Mexico.
Whom are you calling the Prophet: Senator Obama, Senator McCain, or President Bush?
It’s not for me to give away other authors’ plotlines 
Heinlein, to at least give us an outline of how the Lazarus Long epic concludes.
See the OP already has mine. I’m so desperate for more of Middle-Earth I just role-play there instead. I think it is more fun than fanfic and besides I am a poor writer.
BTW: Heinlein is my second choice, but I want him resurrected and placed at age 45 or so when he was at his most prolific.
Well, we’re resurrecting him; of course we’re also rejuvenating.
And taking him out of the grave as well. Otherwise nobody’s getting any work done, as they’ll be screaming “Let me out! Let me out! You BASTARDS!!”
Except we already know, of course; it’s as complete as it’s going to get, anyway.
At the end of TO SAIL BEYOND THE SUNSET, Lazarus has reconciled with his son Colin Campbell and brought his grandfather back alive from the past; since Maureen is already resurrected, hot, and sleeping with him, his incestuous family is complete. And based on Woody’s meeting with the prophet-scientist from “Life-Line,” I think it’s clear that he never dies.
I always thought the the Guide-Bird was powerful enough to fulfill its orders, and then put reality back any way it wanted. The next book could be a sort of teenagers vs adults plot, with the Book and Random being the teens. Writing it would be the reverse of the problem he had after the first episode of the radio program.
At the end of the radio program, Ford and Arthur had been thrown out an airlock in the depths of space. DNA said he hadn’t expected the program to be picked up and therefore hadn’t planned a way to save them. He couldn’t think of any way to do it that wasn’t ludicrously improbable. We know where he went from there.
In a hypothetical sixth HHGG, he’d have a nearly omnipotent character and how do you choose what it will do when anything is possible? It’s like picking out a flavor at Baskin Robbins 10^31 flavors.
Better to go to Avogadro’s Ice Cream. They have 6.02 * 10^23 flavors.
Robert Anton Wilson to finish the Historical Illuminatus Chronicles.
Avram Davidson to write that promised Doctor Eszterhazy novel (all published of the Eszterhazy corpus is short stories). In particular, I’d like to see Eszterhazy in love.
Yeah, but what of Boscone? (It’s been a long time since I read the last few books, but I recall this being a major open question.) Who is it, what is it, why is it doing what it does? I never really cared too much about all the bizarre incest stuff…
Aw, heck. I just realized I’ve a much, much better answer:
one of the authors of the Gospels. any of 'em, really. or, Paul, failing that. or John of Patmos.
Steinbeck, to finish The Acts of King Arthur and his Noble Knights.
Shakespeare, to do a trilogy of plays about King Arthur.
What you don’t know is that Jordan in fact died in 1990 but, as per the OP, was brought back from the dead for the purpose of finishing his Wheel of Time series. When this was explained to him, he replied, “Then this series is never going to end!”
Cordwainer Smith, to write anything else set in his ‘The Instrumentality of Mankind’ verse, which is some of the most unique SF I’ve ever read.
Age 53, only one novel and thirty-two short stories. 
Lewis Carroll, to write a third Alice book.
H. Beam Piper, to write anything he wants. Fuzzy, Para-Time, Empire, anything at all, just make it long.
I, too, want Heinlein back, and writing at least a few more juveniles, and shorts.
Heinlein had already plotted out this story, and even titled it. You can see it on the timeline for his future history that was published with some of his story collections: The Stone Pillow. Which means the plotting and mechanics had been worked out (to some degree) at least as far back as the mid-fifties. I think it was in Expanded Universe that he gave a bare bones outline of the story, and then admitted that he really had little desire to write what was going to be such a bummer of a story.
I’m not sure that even with Skald’s reverse switch and time limits you’d be able to convince Heinlein to write any thing he didn’t want to write.