It's also not completely implausible that Manchin could lead the WV legislative Democrats back into majorities (though the House got pretty heavily Republican in 2014).
The same way that Governor Steve Beshear took back the Kentucky Senate for Democrats? Or how Gov. Jay Nixon took back the Missouri legislature?
Face it, West Virginia is gone. He may be able to hold back the tide a little by keeping the governor's mansion in Democratic hands, but after he leaves office, watch the WV GOP consolidate its gains at every level in the state.