Wrongful "Death"

[Jeunemaitre]

If it was so, then after every death you'd only need to disconnect from the internet without quitting the game first.

Not necessarily-
There may be a "recieved death notification" trigger that is sent when the cleint machine puts up the death screen. If disconnect happens between the killing blow and the trigger, then the server resets the character and gives the benefit of the doubt to the disconnect timing (in a "tie goes to the runner" sort of rule). However, when have we known the wonderful folks at Blizzard to be benevolent (No we can't bring back your HC character, so don't even ask, la la la, we can't hear you...)