If the GOP should win majorities in both houses this November, they are unlikely to have enough votes to override an Obama veto. So, the most a GOP majority will be able to accomplish between now and January, 2013, is to forestall further mischief.
The mischief already accomplished by the Dems will sit there festering in the body politic for a minimum of two years, and maybe longer. The public will have that long to get used to the health care "reform" bill and whatever other bad things the Dems manage to push through between now and January, 2011.