Seems like an important element of the episode that they forgot to put it, but hey it happens. At least they clarified it, the wonders of Twitter I suppose.
I must admit it was a difficult to look over Marco dedicating himself so readily to the quest, given how long he was on it and how he's usually the one to accept negative results and look for help from either the original source or an authority figure. Just assumed it was cartoon logic and put it out of my mind.
Sadly I would imagine that Marco retaining much from his time there is unlikely given the influence of magic over him, makes it easy to go back to the status quo.