I was under the impression that EventHandlers don't work correctly in Multiplayer.
Assuming that you're using a
Lone~Wolf style method, what you want is a filter script to intervene. Again you need a trigger covering all units set to Anybody, Present, Once and the On Activation field to read:
{_x exec "filter.sqs"} forEach thislist
{_x exec "removalscript.sqs"} forEach crew _this
This will cause the script to be run solely on units, if you want old vehicles / armour to be removed along with their dead crew you'll have add that to
removalscript.sqs.