Assuming that the vote is strictly party-line, how would this end up looking?
Using Larry Sabato's ratings for House races (probably not the best, but the most amenable for a quick analysis of this sort of thing as he actually lists the safe districts):
Romney appears to have 24 states in the bag already, to Obama's 11:
Some of these "tossups" lean heavily in one direction, however. Kristi Noem (SD-AL) won narrowly over Herseth-Sandlin last time around, but is not facing her again and has the advantage of incumbency; other sites list Noem as safe. If we give SD to Romney, that puts him at 25 states, one state away from victory. North Dakota's and Montana's current Congressmen are both retiring to run for Senate, but their seats are likely to remain Republican. If just one of them remains Republican, Romney has 26 states and the Presidency.
Other possible Romney states from the remaining `tossups' are Michigan (they would need to retain MI-3 and MI-11) and Wisconsin (they would need to retain WI-7 and WI-8), probably followed by New Hampshire (where they would have to win both seats).
All in all, the House is basically
Safe Romney assuming no defections. Considering the only strongly Obama state in the above is Pennsylvania (which Romney doesn't even need should the Republicans hold onto Montana and the Dakotas), such a possibility seems remote.