Yikes - I know a guy who just bought a house near Van Dorn Street metro and he's screwed now. At least people in Old Town can take a bus to Crystal City and people at Franconia-Springfield can take VRE.
I'm very fortunate to have ended up living in a neighborhood with excellent bus service.
He can probably take the DASH bus to King Street. I believe one of the routes that serves Van Dorn also serves King; there's also a route along Pickett Street that serves King (a former colleague used that one, so I know of it, but I don't know details). The VRE stops at the Amtrak station at King Street, but the VRE fare is pricey at $7.00 one-way. (The Fairfax Connector runs from Van Dorn to the Springfield Metro, but that takes too long to be a realistic option if you're headed inbound via the VRE. Makes more sense to go to King.)
I think there may be a DASH bus route from somewhere in the Landmark area that serves the Pentagon, too, but I'm not sure. Easy enough to find out, though.
I live off Van Dorn south of the Beltway in Kingstowne. Don't know what my work situation will be next summer, but the thought of using the Green Line from Branch Avenue has crossed my mind, as has the notion of picking up slugs. During SafeTrack, there was a nonstop Fairfax Connector route from the Springfield Metro to the Pentagon Metro via the I-395 express lanes. Hopefully they do that again, because this time I'd use it. Last time my wife and I just drove, but she's no longer working downtown.