well without using a trigger, what you could do is create an array for all west players and all east players
eg lets say its a 24 player game
E_array = [E1,E2,E3,E4,E5,E6,E7,E8,E9,E10,E11,E12]
W_array = [W1,W2,W3,W4,W5,W6,W7,W8,W9,W10,W11,W12]
E1, would be the name you gave to one of the east units in the editor view
you could then count how many units are alive in each array
remove all elements of the array that are not alive
resize the array
and then return the list of all name _x in the array
if you needed to do this further into the mission than right at the very start, then you would have to update the arrays every time a player respawns, remove the older elements of the array that the dead player element became and replace itr with the newer element
See kegety's spectator script for some ideas on what the script lines look like to do some of this
I know its a bit vague, but without specifics as to when and why you need to do this, then the answers are vague