My money is on the Marshal returning later, but becoming an actual Mandalorian. Dude is very skilled, honorable, has no qualms about deadly situations, he's a perfect Mando candidate. If Din can't find more Mandalorians, then he can make some.
Wouldn't help his quest with the Child, but I want that to happen regardless. The Marshal was too badass to be abandoned by the storyline.
I'm not counting his appearances in the Aftermath books, because they suck.