I don't think that's the key. I think there are two keys:
a) the $1.5 million. Given where the budget is at, is recouping $1.5 million important? And will there be some way to reinvest that money in a better risk than Stewart? (Actually, it's probably more like $1, since you'll have to pay major-league salary to the guy who replaces him.)
b) VORP/scouting/25th man/4th IFer. If you cut Stewart, that enables you to carry somebody else on the roster as your 25th man. Will that person, whether Maysonet or whomever, be as good or better risk than Stewart? Does Stewart have any value, and if so how much, over the guy who replaces him?
4th man: There are 486 games total between 2B/SS/3B. Valbuena, Castro, and Barney won't play all 486, somebodies will need to fill in the "X" missing games due to injury, rest, or failure. If Stewart ends up staying, he might be used ahead of Lillibridge/Maysonet/Watkins. With Stewart among the top 4, Valbuena's and Barney's positional flexibility would allow Sveum to adjust for an injury or a major slump by any one of the four. But if Stewart gets cut, who's going to pick up the "X" out of 486 that Castro/Barney/Valbu don't? Lillibridge/Maysonet/Gonzalez.
So is it worth the $1 to have Stewart available among the front four or not? That's key.
The question of Stewart versus Valbuena as the 3rd man is interesting, but I think it's really the question about Stewart versus the replacement 4th man that determines whether they cut or pay Stewart.