Guys, Clive Cussler is a good writer. I'm not sure what your problem with his book is all about. In fact, he wrote it so well, all you need to do is think up a new way to threaten the world, research another important shipwreck of the past, and come up with a new way to tie said shipwreck into the solution for said threat, and you get to read it again, but for the first time! You could read this book for the first time more than a dozen times, maybe two dozen, before you exhaust what it has to offer. Clive Cussler has written a masterpiece of a novel.
I really like his books, actually. It's not the sort of thing that you read for posterity, but it's still time well spent in its own way.
I would want Tom Robbins to survive, but his legacy will only live on through word of mouth. Unless some revolution in US culture puts his books into literature classes, his work is probably not going to get any public recognition after he is gone. Likewise Robert Anton Wilson.
In terms of sci-fi, I definitely think Isaac Asimov, Robert Heinlein, and Arthur C. Clarke are going to survive past the 20th century. Philip Dick will, if there's any justice in the world. William Gibson might make it too. Within the sci-fi genre they will be the equivalent of Austen or Dumas for at least a couple centuries, but this is true of other writers as well ... I'm only including these in specific because they wrote books that were important across genres.
J. K. Rowling is really the only fantasy writer I'd put on the list. People will be reading her books 50 years from now for sure, and maybe longer. And Neil Gaiman has an impressive enough portfolio to give him a lasting name.
In terms of current or recent novelists/writers, I'd look at Thomas Pynchon, Don DeLillo, Philip Roth, Kurt Vonnegut, Toni Morrison (unfortunately), Alan Moore (yes, I think he counts, and yes, I think he'll stay important), Joseph Heller, Hunter S. Thompson, and maybe Chuck Palahniuk if he's lucky (although his books, along with most I've mentioned, will be as dated as Treasure Island in probably less then 60 years).