I guess if the season were to start again on November 1st, Danny Espinosa would be the second baseman. Backing him up would be... I don't know. Frandsen? Kobernus? Probably Frandsen.
Reasoning on Presumed Plan : It's hard to figure what the Nats want to do at 2nd base. It's tough to believe that they really want Danny Espinosa to be the starter. They didn't want him to be the starter at the beginning of 2014. Rendon was at 2nd base then and was forced over to third by Zimm's injury. They didn't want him to be the starter at the end of 2014. Cabrera was brought in by trade to play 2nd base for the stretch run.
At the same time right now Danny Espinosa is the best 2nd baseman on the Nats roster. Cabrera is a free agent. Rendon is not going to be moved back. Danny is clearly better in the field than Frandsen and Kobernus and as bad as he was at the plate, he was better there too. He's super cheap, thanks to the minor league re-visit he won't be a FA until after 2017. Therefore right now he's the presumed starter.
As for the back-ups, the Nats love Frandsen. He doesn't cost much and... did I mention they love him? The Nats are pretty devoid of upper level minor league MI talent so Kobernus is mentioned as an alternative by default. If you want to push for the seasoned failure Emmanuel Burriss or the walking organizational filler, Cutter Dykstra, be my guest. The Nats are big on Wilmer Difo who looks to be at least an acceptable level major leaguer in the making so you could say they will let Espy play this year with the hopes that Difo will come into play during 2016.
Problems with Presumed Plan : Danny can't hit. Or more precisely he can't hit left-handed. His splits are telling
LHB : .183 / .241 / .291
RHB : .301 / .374 / .485
Now Danny isn't .300 good, but he has always been better hitting righty. He does lose his homer pop, but the increase in average is dramatic enough to make that up and then some. So why not just platoon Danny? Well, it's easy enough to say "Oh well then Danny only bats versus LHP" but if you are going for a platoon here you just made Danny the smaller part of the platoon and forced yourself to go out and get the better part. Maybe you can find a lefty-masher but a righty-masher? Those usually are called "starters" because there are a lot more RHP out there.
Danny also has a big strikeout problem. It's an issue right-handed (22% K). It's a career-killer left-handed (39%) If you are forced to start Danny and he bats as normal - you are looking at a below average bat. At 28 in April there's little chance he will get back to the level he was.
The back-ups meanwhile, not only can't unseat the below average Danny, but you don't even consider it. They are bad back-ups creating a "true hole" for the Nats positionally. Frandsen is a contact hitter but that's it and he can't field. You can't trust any minor leaguer to hit even to Frandsen/Danny level.
The Difo plan is interesting but you'd be throwing away 2015 as there is little chance he'd see the light of day this next season. I'll remind you that this is a win now team. Plus he is a SS, making him Desmond insurance in case the Nats let Ian walk. He can't replace both. (I'll add I'm not nearly as high on this guy as other people).
My take : Danny Danny Danny. Should have gotten that surgery.
It wouldn't be the worst thing if Danny started for the Nats. He can field and he can hit lefties. The issues is what to do with a righty on the mound. On that I agree with the Red Porch Report. Force Danny to give up switch-hitting. It may not work, but he hits so poorly from the left side of the plate that it's difficult to imagine it being worse. If it is worse - if he puts up a completely empty .120 or something - he can always go back to hitting .180 with pop. But you have to try.
Still I have the Nats in win-now mode and in that mode you don't settle for "wouldn't be the worst thing". To me, Danny starting with no switch hitting, that's the barely acceptable back-up plan. Plan A should be going after Ben Zobrist. Zobrist is old, but he's a good fielder, has patience (his 75 walks would easily rank 3rd on the Nats), and is a better contact hitter than almost every Nats hitter. He's old (34 in May) and his power is going fast but the Nats are only concerned with 2015 and given his performance has been down from his peak for two years and he's close to FA the deal shouldn't be overly costly for the Nats unless competition forces it up.
Why no one else? As per usual in this modern age of locking everyone up young (why the youngsters are going for this is beyond me - you're selling yourselves short boys for security) there isn't much out there for the Nats to go after. Free agent wise there REALLY isn't anything (unless the Rays just don't sign Zobrist and that would be stupid). Trade wise the Nats are in a bit of a disadvantage. There are 3 decent targets who will be up for FA after next year, but two are in the Nats own division. Assuming Murphy and Utley won't be traded to the Nats that leaves Zobrist.
Usually the Nats might eye a decent cheap player with more than just a year left but there isn't any. Altuve and Dozier fit the bill but have contracts too reasonable to imagine they'd be dealt for anything but a big return. Everyone else is either on a team that can't afford to give them away or too expensive to think the Nats would deal for them. I suppose that maybe Howie Kendrick could be dealt. The Angels are looking for young pitching and he is a FA after 2015 but I'll hold off on believing that until I hear something about that because it would be an odd move for the win-now Angels.
So I say trade for Zobrist. Make Danny the Back-up.
Outside the Box Suggestion
Move Rendon back. I could come up with several different scenarios involving trades and position switching and the like but let's get down to brass tacks here. It is harder to find a decent 2B than a decent 3B. This is true in FA. It's true in the minor leagues. Anthony Rendon played 2B just fine. There's no way around it. What's best for the Nats is that Rendon moves back to 2nd base.
What happens at third? I don't know this is a 2nd base post. Trade for Beltre. Sign Sandoval. Throw a (small) busload of stuff at the A's for Donaldson. See if you can get Ramirez cheap, if he goes to market, or Headley super cheap. All I know is you have a great hitter who can play 2nd base and you're moving him to third because that's his 'natural position'. That's all well and good but it's not giving you the best team on the field.