I always wondered if you somehow attached a person to a type of rope and had them go through the veil, would they be able to be pulled out? Do they immediately disappear when they go through, so it wouldn't matter? I assume that this is the type of thing they study in the Death Room. Also, if you were restrained so you couldn't be forced to go through the veil by the thrall of the veil, what would happen if you pulled the veil aside? Would you see the other side of the dais or blackness?
Within the Harry Potter universe, it seems pretty clear that once someone is really and truly dead, there is no coming back. Even if you were able to retrieve their body, they would still be dead.
However, I do not believe that the rope would be of any help. I think that if anything that passes the veil is irretrievably gone and that all you would end up with is a stump of rope.