Really? It's an open and shut case and he gets compensated. That's a no-brainer. If anyone thinks it's easy to just copy a game and expect no repercussions, you're wrong. And it doesn't matter if the author seems to care or if he abandoned it. It's still his own game and unless he licenses the content (or even just the concept), he's free to ignore it while nobody is free to remake it.
Even if the game is ostensibly abandoned, the creator might be talking with a potential licensee behind closed doors and in such a case, if you copied the game and benefited from it, you're completely screwed.