It would be bad, but I don't think it would be that bad.
It has taken over seventy years to address the nonsensical readings of US vs. Miller. The Miller decision unreasonably limited the right to weapons USEFUL TO A MILITIA. Anti-gunners since then have purposely mis-read it to limit the right to MEMBER OF AN ORGANIZED MILITIA.
The Heller decision clarifies that individuals are protected and broadens the purposes to include self-defense.
Even the Supreme Court knows that the 1994 election handed Congress to the Republicans because of gun control. A Supreme Court decision REVERSING Heller could very well start a civil war. And for what? So politicians can claim that they are doing something about crime?
An Obama Court will probably content itself to letting bad decisions stand and attempting to reverse good decisions so that they go no farther than Heller dictated.
Only to have it replaced with a different nonsensical reading, this time by Scalia no less. Scalia reads the 2nd amendment as permitting the government to ban the private possession of M-16's, based directly on a dishonest construction of Miller.