I think MSL may have been in play to an extent, but I maintain that the idea of a one for one with Callahan was probably a bad interpretation of what Boomer may have been told. Even if St. Louis forced Yzerman's hand and said "I'll only go to the Rangers" there's nothing forcing him to take action on it before the trade deadline. Getting a UFA that you have no intention of re-signing isn't fair value for MSL, even if he's 38 years old.
The Pens are pretty happy with MAF this year. They're confident that the difference maker is a much improved blue line which will take some of the load off of MAF. They've been shopping for scoring since Dupuis went down (dangling Despres, who has a bit of a Torts/Kreider thing going with Bylsma), even though Martin and Letang will miss a lot of time, they're still pretty confident that Scuderi/Orpik and Maatta/Niskanen can anchor the top-two pairings until at least Martin returns.
The real issue for the Pens is that outside of Despres, they're really thin on assets that they can, or are willing to trade. The Pens organizational depth is really on defense, and Buffalo is loaded with young D already. The Pens also have no cap space to work with unless they put Letang on LTIR.