My apologies for not reading your question properly in the first place.
Dead men don't speak.
If this is a single player mission then it doesn't really matter if you use groupchat, sidechat, or globalchat - the only difference is the colour of the text.
If its a multiplayer mission you're in the wrong place - ask the mods to move this thread to the multiplayer board.
You could name all the loons in the group and make a script something like this (this is not a perfect script, its just a sketch of what you could do)
#loon1
? not (alive loon1): goto "loon2"
loon1 groupchat "text here"
exit
#loon2
? not (alive loon2): goto "loon3"
loon2 groupchat "text here"
exit
#loon3
etc