Honestly, I don't think you've addressed my points at all. And Faldage merely said it was a preposition being used adverbially. He didn't say why or how, and you're just saying that you're with Faldage.
Clearly, prepositions and preopisitonal phrases can be used as adverbs, and I provided some examples. I just don't think that in situ really qualifies, either by the rule of having an object or not, or by the rule of "if it sounds funny to hell with it." Given that in situ translates as "in the place," it clearly has an object. So unless somebody can show me a usage that is akin to saying "Get out," "Go west," or "Drive south" then I'm unconvinced of its claim to adverbial status. I would also accept a usage that met my own criteria, one that had an object but still clearly modified the verb itself.
