As ridiculous as this sounds, there's certainly historical precedence. After all who did Fred idolize? The Dodgers. And what did the Dodgers do? Moved out of NY.
So the better question is, if the Mets were to move to Montreal, which National League would jump at the chance to move into to the NY market? Which team would you want?
That said, I dont believe the Mets would move to Montreal in a billion years.
"Mr. Martin Tanner, Baritone, of Dayton, Ohio made his Town Hall debut last night. He came well prepared, but unfortunately his presentation was not up to contemporary professional standards. His voice lacks the range of tonal color necessary to make it consistently interesting. Full time consideration of another endeavor might be in order."