In the case of phrases like this one: "mit oder ohne dir", which case is "du" supposed to be in? Are both dative and accusative acceptable? If not then how do you determine the right conjugation?
I'd say: "mit dir oder ohne dich". You need to double the "du", otherwise it sounds strange.
of course "mit" needs the dative and "ohne" the accusative, so by repeating the "du"-part the sentence "mit dir oder ohne dich" is grammatically completely correct. In spoken language you will, however, often find a contraction, which is grammatically not correct, but sounds smoother. In this case you will use the case of the second preposition, i.e. "mit oder ohne dich".
Don't know, but I heard it on a news broadcast and it's akin to Eng. "with or without you".