Fed ex field site says concert should end around 11.15pm.
Last metro leaves at 11.27 and it's a mile from the stadium. You'd need to give yourself probably 40 minutes to get out of the stadium and walk down to the station to comfortably make the train.
I'm not missing that much of the concert so it looks like ridesharing to get back to DC. I'm in SW so anyone in my neighborhood or on the Hill, if you want to somehow carpool/ridesharepool back let me know.