Group any civilians with a BLUFOR soldier with a higher rank (so that he is the leader) and change his condition of presence from "true" to "false" (or . This will make the civilians part of the WEST side, so that they will be killed by OPFOR on sight.
Create a large trigger that covers the whole map (or at least all that there are civilians in). Set:
Activation: BLUFOR PRESENT ONCE
Condition: ({ _x isKindOf "Civilian" } count thisList) == 0
Type: END #1
(Oops, Cheetah beat me too it).