If a Logia user dissipated before they were hit by a Haki user instead of as they were, would they still be hit?
yes
Didn't Iceman open up a hole in his chest so he could avoid Whitebeards hakistab?
They probably get reformed at that spot if they didn't get too far. Like, if Rayleigh punched Smoker in the jaw as he was smoking away, his jaw would probably form back to get his, along with the rest of him as he lost concentration.