By text do you want it for a script or a trigger?
For a trigger try this in the condition field
({alive _x} count [unit1,unit2,....]) < 1
For a script try
if ({alive _x} count [unit1,unit2,unit3,...] < 1) then {end1 = true}
Syntax not tested.
There are other ways. You could give all your guys a "killed" event handler that runs a script whenever any of them get killed that checks how many are now dead.