If the GOP wins the Senate (and therefore Congress, more or less), the White House is less needed to certain extent, but if Obama wins the Presidency and the GOP wins back Congress, that will make for an awful 4 years.
Obama has already made it fairly clear that he does not govern well - or really, much at all - unless he has full wind at his back, i.e., Democratic majorities in both Houses. Whe he can't get things done through a compliant Congress, he takes his ball, goes home, and tries policymaking through the executive branch. Even Democratic lawmakers are beginning to publicly complain about this.
But here is the thing: if Obama wins the Presidency and the GOP wins back Congress, each can claim a "mandate". The GOP will say "we won back a majority precisely because the American public wanted us to go a different path than the Obama-crats", and they will be emboldened with big legislation or big standoffs with the President. Obama will say "I was re-elected president, so the public clearly wants me to keep charging forward with my vision", and he will do even more outside of Congress (executive end-arounds) and lots of vetoing.
This could be a mess. Now, I am usually one who favors a little bit of divided government - it has a way of putting the brakes on reckless legislating - but given the crises that we face, and because these crises were exacerbated by the Obama-crats (not to be confused with all Democrats), we need some very important, timely legislation to be passed soon, and the kind of divided government we'd have with GOP-Congress and Obama Presidency would not be good.
Compare to Clinton - he was a centrist, and post-1994, he became more of one and was able to work with a Republican Congress, with everyone sharing in some of the glory of accomplishments, but at a minimum, he remained relevant to the legislative process, even as the prerogatives and the priorities of the legislation became more conservative (as reflected by the 1994 shift in Congress).
There's not much indication Obama is capable of the same, and that would be mean a very partisan, do-little 4 years, I think.