I know that it's been 200 years since Oblivion, but there could ALWAYS be something stupid, funny, and downright insane. If it beaks immersion than fine, his
quotes broke immersion. If you want to be realistic, than just ignore him. Perhaps he found a new Heart of Lorkhan? Or maybe he received immortality as part of Sheogorath's favor? Or he could have killed enough Mudcrabs to earn it from the TES community. Or it could be a new M'aiq, and it works kind of like the Grey Fox, passed down from M'aiq to M'aiq.
Face it, almost everybody enjoyed finding M'aiq the Liar outside of the main gate at various towns in Oblivion (IDK where he was in Morrowind, never found him). I wanna 'nother M'aiq.
EDIT: And if M'aiq IS in Skyrim, he had better have a quote going something like "There are a bunch of dragons flying around, ARE YOU HAPPY????"