Adam Eaton has been so good and so important for the Nationals this season and losing him is obviously a huge blow. The only positive for the Nationals as a team, is the timing of Eaton's season ending injury. I feel horrible for Eaton, he was playing so well in his first season with a good team and finally starting to get some of the national attention he has long deserved. With that being said, losing a key player early in the year is probably the best time something like that could happen as it gives their team plenty of time to figure out the best way to replace them.
From what the Nationals have said it looks as if their plan is to use Michael A. Taylor as their every day centerfielder and while he certainly deserves a chance, I have a hard time imagining a scenario where he plays well enough on a consistent basis to be worthy of that roll. However, there aren't many other options based off what the Nats currently have on their big league roster. Personally I like the idea of putting Trea Turner back in CF and using Wilmer Difo as the everyday shortstop. Difo has shown that he can play consistent defense and while he isn't a great offensive player, his .222 AVG and .314 OBP is far better than Taylor's .192 AVG and .214 OBP. Another option would be to keep Turner at SS and play Adam Lind/Chris Heisey in leftfield with Harper in CF and Werth in rightfield. While this would potentially provide for more offensive production, I think it gives the Nationals a far worse defensive outfield. Lind/Heisey would be average at best in LF, as would Werth in RF and while Harper absolutely could play CF at a high level, it leaves him at too much of a risk for injury. Staying within the organization, Brian Goodwin who had 42 ABs in the big leagues last fall and is currently in Triple-A Syracuse, is an option to help fill in; as is Victor Robles, the Nationals' 19-year-old top prospect, but he's most likely not ready for that type of pressure.
As I said before, the Nationals do have plenty of time to figure this out and I'm sure they will try many different things to help deal with life without Adam Eaton. If none of the options currently in the Nationals' organization work out, a trade could be a possibility. Two big names to keep an eye on are Andrew McCutchen and Lorenzo Cain, of the Pirates and Royals respectively, both will most likely be involved in trade rumors as the season goes along but will most likely demand a high return as well. Cain's contract expires after this season and McCutchen has a team option so either of them could leave after the season allowing for a smooth transition back to Eaton next spring.
Whatever the Nationals do they most likely will not be able to fully replace Eaton and will have to hope Bryce Harper, Ryan Zimmerman, Trea Turner and Daniel Murphy continue their early season success. Luckily, the Nationals do have a deep lineup to go along with elite starting pitching and on top of that, they play in a relatively weak division. It won't be easy and Eaton will be greatly missed but at least the Nationals have time to figure this out before a (hopefully) deep playoff run this fall.