Enid Blyton, I think she would write a first class DL book.

Wayne Van Zwoll -the story would most likely be shite but at least the gun facts would be acurate !

Jim

Brian Keene expressed an interest several years ago in writing a Deathlands book. I think he would be an excellent fit, at least for one go.

Edgar Rice Burroughs and Robert E. Howard. Could you imagine?

Matthew Stover, perhaps. David Gemmel? Larry Correia. Greig Beck could make an excellent Outlanders adventure. His Arkadian series proves that. 

 

There are also a couple of western authors I sometimes read that would fit the bill perfectly, methinks.

Weston Ochse, author of Blood Ocean and Seal Team 666 would be a very good fit.

Asimov. Can you imagine?

That would certainly take some doing, what with him being not-alive for more than twenty years now....

Although I see now the original question did say "living or dead". I have failed in reading comprehension. ;-)

I would choose Frank Herbert.