I have a copyright question related to "What-ifs"
Sequels and such based on Twain's works don't
seem threatened by any copyright issues,
but what about more recent writers,
say Hemingway or Fitzgerald-or even Sylvia Plath?
Would the freedoms granted satire and parody cover pretty much
anything one wanted to do?  Or would there be serious pitfalls?

I've always seen these "what-ifs"-- I've written some myself--as
fascinating thought experiments and, really, a kind of homage to the
author's characters: proof they have transcended their time and space.
I've used them to get my high school students more interested than they
might otherwise be.
These efforts do require knowledge of that time and place.   (My own book
placed Huck in the Civil War, and CW scholars are another very tough room!)
I haven't read Oates's work or the recent BECKY, but I confess I
love the genre.

Dan Walker