"In short, the Solodyn patent does not expire until 2018 but is useless and they know it."
Yes an no. The patent can still be effective even if it doesn't preclude the FDA from acting. Hatch-Wacman has no effect on patent rights (other than precluding a holder from suing to prevent FDA action).
The question or marketing the aproved generic will be for the courts to decide (if MRX goes that way). It is certainly possible for an FDA aproved generic to not be marketable due to patent issues.
You may be right in the particular example, since the only aproved patent held by MDX is not for the drug per se, but for the formulation. Thus, the generic may very well not be ifringing THAT patent (you still have some pending patents that might apply according to MDX).