The charged unit dies before combat
No, they do not get any additional movement. 

What happens is the unit is not engaged in a combat, so it does nothing in the close combat phase.

I assume you are thiking of the Overrun rule? Where if you wipe out a unit in close combat on the turn you charge you get to move another 2D6" forward afterwards.

The rules for Overrun (8th Edition Rulebook, pg 58) specify that a unit only gets an Overrun if "all it's enemies have been wiped out as a result of the combat". So if the opposing unit was wiped out before the close combat phase began, they would get no Overrun move.