The Nationals are reportedly still in talks with Adam Laroche in an attempt to re-sign him. Of course, they don't have a deal yet, so it is not clear whether or not he will be returning. So if we played a little "what if" game and assumed that Laroche wasn't returning, what would be the Nationals options at first base? The most obvious option seems to be platooning Tyler Moore and Chad Tracy.
Another more inventive option, especially if they believe Anthony Rendon is ready, would be to move Ryan Zimmerman and his ugly throwing motion to 1st base. When you look at their minor league options from 2012 (using Baseball Reference's organizational depth chart), most of them weren't pretty. Mark DeRosa's (who was with the big league team in 2012) baseball career is probably over, Mark Teahen wasn't an option and signed elsewhere, Jason Michaels was terrible in AAA, AA first baseman Tim Pahuta is 29 years old, and Justin Bloxom is not ready for the Majors (at least not according to a cursory look at his career path/statistics). Enter an interesting 3rd option, one that the Nationals turned to, unsuccessfully, in 2011 for a short time:
Chris Marrero was a 1st round pick (15th overall) in 2006, and was even ranked as the 27th best prospect in baseball, despite playing mainly 1st base, by Baseball America in 2008. However, he struggled in 2011 (-1.1 WAA in 31 games) when he reached the Majors, and has had major injury issues. This combo caused Marrero to not reach the Majors in 2012. In fact, he played in 5 different minor league levels in 2012. He played just 53 games in all (37 in AAA) in 2012, thanks to a hamstring tear. In 2008, he broke his right fibula.
With that kind of injury history, there is not many empirical reasons to believe he will be healthy in 2013, though he was pretty healthy through 2009-2011. As a first baseman (he played the corner outfield positions before his injury in '08), he obviously lacks speed (2.0 speed score in 2011 in AAA, 2.5 in AAA in 2012), and he doesn't seem to be a good defensive 1st baseman either with bad FRAAs in 2012 and most of his career in the minors. With the bat, his 2012 was a disappointment, as he was terrible in AAA. In 2011, he was solid in AAA (129 wRC +, tied with Matt Hague), but not overwhelming for a first baseman, 6th in the International League. However, he was younger than all of the players above him. In fact, in 2012, no IL player 22 years or younger had a 129 wRC + or better (Starling Marte was 23). Dayan Viciedo was better in 2011, as was Jesus Montero and Freddie Freeman (both 20) in 2010. Obviously there are mixed results in the Majors with those players so far (Dustin Pedroia was the only player 22 years or younger with a 129 wRC + or better in the IL in either 2006 or 2007), but it does at least give the impression that Marrero was some kind of prospect before the 2012 injury. He has always been a guy with elite (or at least nearly elite) power but his reputation is of one that has struggled with breaking balls. The latter certainly played out in the Majors, as he struck out 27 times and walked just 4 times, with 0 homers and 5 doubles. His swing at the plate definitely needs a lot of work, as he keeps his hands low, and it really affects his swing path, which is not one you would expect from a power hitter. According to his swing maps, he was very aggressive (3.58 P/PA, which stabilizes very quickly), and had some serious holes in his swing.
Marrero is not really an option for 2013 for me. He should start in AAA while the Nationals exercise one of the options listed in the above paragraph (and exercise Marrero's 2nd option). In the minors, Marrero has been significantly better against lefties than he has against righties, especially when it comes to K/BB. Unfortunately, when he was in the Majors, he had to face a lot more righties than lefties. He may turn out to be just a platoon 1st baseman/pinch hitter or he could even be a AAAA hitter. He has put up legitimate numbers in the minors despite having serious holes that stop him from being a big league player. This, and the injuries that will continue to keep him off the field/diminish his skill set, really makes it hard to be a big fan of Marrero.