I have heard that another party is already in the works, but I don’t know anything about that, or even which party, libertarian maybe? If you think that legally he can’t because he will have lost the primary, that doesn’t apply in presidntial races, just the lower ones.
If he does run (I cannot imagine him winning, but I never say never), I think he’ll draw more voters from Obama, than Newt. The democratic Party is far larger than the Republican Party (Last I read, something like 70 Million to 55 Million or so, but both have been losing members for about a decade, very fast since 2008), so it will be up to the Independents to decide the election. They already don’t like Obama, so it will be up to the Republican to prove he’s going to be a significant enough of a change to support him. I think Newt would, Romney certainly wouldn’t.