I believe that, if it's a hung jury, the prosecutor has that option. I refuse to call him special right now. He's been an absolute jerk.
Clearly the government would have the option. But would they?
It seems to me the only reason to try a case like this is if Fitz has bought into the whole conspiracy angle .Libby is obstructing justice about what? a bunch of media induced gossip or some huge sinister plot. (it has to be the sinister plot or why bother)
So if Fitz is a true believer and if the trial is deadlocked he will go after Libby again.