Kirby obviously didn't feel hard done by enough to stay gone, did he?
He came back after he left Marvel.
There's a lesson to be learned there; leave that which you end up disliking. The great Kirby didn't stick around at Marvel to whine about how he was getting treated.
Even so, the beefs he allegedly had were nothing to do with money, but misplaced credit. I find this odd, considering he's pretty much as revered as Stan Lee. More so, maybe.
He signed over many of his rights to Marvel, so he wasn't living on the breadline financially.
-AC
Jack Kirby's heirs want a piece of Spider-Man