It would depend on the reason for Romney's collapse. Does he collapse with fis-cons or with so-cons? The most plausible scenario for an Obama landslide to me would be that Romney makes a full embrace of the Akin comments and the bottom falls out for him in the fis-con suburbs. My map of this would be:
It would be more like the Johnson landslide than FDR or Nixon. Most of the national swing is driven by very high Obama margins in CA-IL-NY. VA would fall behind the national margin in a landslide and NH would zoom above it. I just don't see the interior South voting for Obama under any circumstances.