While negotiations with Adam LaRoche and the Boston Red Sox never appeared to be serious, they won't exist in any capacity starting now:
Source: The Nats have agreed to terms with Adam LaRoche on a two-year deal.
— Adam Kilgore (@AdamKilgoreWP) January 8, 2013
Since the Red Sox are likely ending up with Mike Napoli anyway, maybe this isn't a significant announcement. But, because one more potential suitor is off the block, and one fewer replacement is available to Boston, maybe this is the push the two sides need to move towards a conclusion in their own negotiations.
It also might help the Red Sox out a bit, as LaRoche, who hit .271/.343/.510 last year with the Nats, had to settle for just two years rather than the three he was searching for. If the Red Sox give Napoli three years as planned, but with language that protects them from a future hip injury for the final year of the deal, then he's, at worst, on the same plane as LaRoche. Unlike LaRoche, though, he'll have the possibility of that third year that the former just couldn't secure from anyone.
Until Napoli officially signs, there is the chance of a trade for Mike Morse, who won't be playing first base for Washington now that LaRoche is back. While the rumor is out there that lefty relief is what the Nationals desire for Morse, that seems... low. He's entering his final year of arbitration, and hit .294/.343/.514 over nearly 400 games with Washington. If something goes awry with the Napoli deal, and lefty relievers are indeed what they're looking for, Boston does have an abundance of them. But you have to think, given Morse's performance, low cost, and the lack of long-term commitment attached, he'll have plenty of suitors available to drive the price up beyond the range of the Andrew Millers of the world.
For whatever it's worth, if I had to put money on who ends up with Morse, it would be the Rays, who are currently playing with James Loney-shaped fire at first base.