It wasn't like Jayson Werth's .581 OPS was helping the Nationals a whole lot, but it wasn't like Jayson Werth was going to hit like that for the entire season. In the previous three seasons Werth has had a .827, .931, and .849 OPS. Any of those would have been great for the Nationals. While they've been playing well without a healthy or productive Jayson Werth there is room for improvement and his loss until at least August is a detriment.
One of the big strengths of the Washington Nationals is the depth of their line-up. If Zimmerman is slumping then maybe Desmond is hot and if Desmond is slumping maybe Span is hot. There are a lot of players on this team who can get hot and be the complimentary line-up piece to Bryce Harper. Anthony Rendon is going to need a bit after coming off the DL to get his swing up to major league speed and until that happens the Nationals line-up is going to lack the depth it could have if Werth were healthy or if they had a more proven left fielder.
When discussing the options for how to fill the hole in left field there are a couple interesting but obvious ones. Danny Espinosa has been one of the best surprises of the season, but when Rendon comes off the DL Espinosa is going back to the bench. Danny Espinosa is also a very athletic individual and left field is one of the least defensively demanding positions on the field. If the Nats want to keep Espinosa's bat in the line-up when Rendon comes off the DL the simplest thing to do is to put Espinosa in left field.
That isn't the end of those options. The Nationals could also put Escobar at first base and shift Zimmerman to left field, a position he played well at in 2014, or they could make a trade for a player on a short term deal. This type of injury is the exact reason the Nationals signed Nate McLouth and why the theory of his contract was much better than the reality of it. Nate McLouth supposedly still can't throw a baseball and hasn't recovered from surgery from last season. This long to recover from surgery that isn't Tommy John's surgery is a little strange. The real point is the Nats have plenty of options and plenty of ways to survive, and soon enough we'll see which one they choose.