Moore bequeathed his share to Neil Gaiman, though I'm assuming Moore, Veitch, Totleben et al retained their rights to their specific contributions.
I have a hard time believing, especially after the legal fight he waged against MacFarlane over the matter, that Gaiman would do something so insensitive to the man who got him started in comics. Which dealing at all with Marvel in this particular matter would entail. Not only does Gaiman scrupulously avoid ever offending anyone if he can help it, I mean...come on. That would just feel vile. And it's a shame because I'll bet it would enable him to finish his part of it.
I can see Gaiman simply staying out of it altogether. It's really a rather awkward situation this accidentally puts him in.