Depending on how bad Romney fails, the Dems could even face net loss from being boned in redistricting in several states. I think it'll be like D+3 or 4 myself but I do no see any scenario short of Obama winning in a decent landslide where they pick up a large amount of House seats.
If Democrats have a net loss in both the House and Senate, it will have been the first time in history that a President was reelected while his party lost seats in both Houses.
Not so. Republicans gained seats in both houses in 1916 while Woodrow Wilson won reelection.