Since there aren't that many unique heroes that resurrect or that many glyphs/powers that resurrect, do we even need the D20 roll here? I'd kind of be OK with him automatically doing that to unique heroes that he kills with that special attack. If we had Event Heroes in there too, that might be different, but since it's just Uniques, I say drop the D20. Also, then in the mirror test, Thanos would be able to own Thanos.
Also, I think Margloth's wording is a good way around the markers here. Just remove them from the game completely and boom, out of sight, out of mind.
I love the auto-resurrection! Much less swingy.
Good stuff here (now we need an Infinity Gauntlet!).