As the Shades can reach Nirn, there must be a finite distance to his moon. Therefore, the time to reach it would be finite, provided that there is a constant velocity.
Personally, I see Mannimarco taking an Altmer form to be an ultimate manifestation of his power; the power to actually reverse transformation into a lich. And presumably visa versa.
I agree. I see there only being one King of Worms. He used his new power to either fix his lich-ness (since as an immortal being of quasi-divine status he no longer needs to be a lich) or simply to regain his original form/appearance before becoming a lich (much like a glamour spell). Possibly the reason he is so weak in Oblivion
(Is he weak or is the CoC really strong and helped by Traven?) is he was separated from his divinity by the jills leaving the "revenant"... yeah I put quotes around it so maybe someone would think about what the word "revenant" means. Revenant of what? A god. That's what.
OR... maybe nu-hatta was wrong and Mannimarco is still a god. The guy we fight in Echo Carvern is simply a weak avatar of a lesser (way lesser) diety. He is just a moon and not a planet after all. If this is the case, then Mannimarco is not dead. He's simply banished. That means he might come back. Ooooh spooky.