In editor
A trigger of your area for count all units, call triggerdetect
In init :
{_x addEventHandler ["Killed", "[_this select 0] exec ""CountDead.sqs"""] } foreach (list triggerdetect)
NbWestKilled = 0
NbEastKilled = 0
CountDead.sqs
? (side _this select 0) == west : NbWestKilled = NbWestKilled +1
? (side _this select 0) == east : NbEastKilled = NbEastKilled +1
It's example with side, u can go deeply in result with group, type etc...