Is it possible he could be even worse than last year? I will always be grateful for the 3 innings he threw in Game 7, so maybe he should be a long reliever. Every 5th day, use an opener and then throw Corbin out there for the middle innings.
At some point, the Nats have to deal with who he is and not how he's paid. If you had Victor Arano go 2 innings, then bring in Corbin, with a hook ready for a stopper along with maybe Espino for innings, that might work.
I don't think Corbin is useless. Even last year, he was good for long stretches of the season. I'm not good enough to figure out what made good Corbin good and bad Corbin bad, but apparently Hickey and Blanco can't figure it out either. Maybe a changed role lets you get something out of him. however, if your goal is to try to get rid of the contract, he probably needs to be at least consistently average as a starter and capable of giving innings.