MrBill

Thanks to all for weighing in on this topic.
I found some of the negative issues in Chump's original code and kept trying to get this all to work.  Here are some key points that I learned:
This death of a group thing is a LOT more involved than the simple Group Dead flag available in the editor.  And I'm only talking about airborne groups here. The checking logic needs to check multiple times and the Bandits are going down in flames. Testing this code took forever as I had to fly to do it...(boo hoo!) 😉 I had a GREAT time working through all this and now have a working script to share. Here's the working script.  Assumes groups are single unit are defined and late activated.  Hope this helps and have fun!
local groupList = {"Bandit1", "Bandit2", "Bandit3"}
local activatedGroups = {}
local function allGroupsDead()
    for _, groupName in pairs(activatedGroups) do
        trigger.action.outTextForCoalition(coalition.side.BLUE, groupName .. " Being checked for death status...", 20)
        if Group.getByName(groupName) then
            return false
        end
    end
    return true
end
local function checkAllDead()
    if allGroupsDead() then
        trigger.action.outTextForCoalition(coalition.side.BLUE, "All targets (Groups) have been destroyed!", 20)
    else
        trigger.action.outTextForCoalition(coalition.side.BLUE, "Some Groups still Alive, Checking again soon...", 20)
        timer.scheduleFunction(checkAllDead, {}, timer.getTime() + 30)
    end
end

local function activateGroup()
    local groupName
    local counter = 0
    repeat
        groupName = groupList[math.random(#groupList)]
        counter = counter + 1
    until not activatedGroups[groupName] or counter > 100
    activatedGroups[groupName] = groupName
    -- if we don't use the counter this locks up in an infinite loop
    if counter > 100 then 
        trigger.action.outTextForCoalition(coalition.side.BLUE, groupName .. " No more groups to activate, waiting for death!", 20)
        checkAllDead()
        return
    end
    local group = Group.getByName(groupName)
    trigger.action.activateGroup(group)
    trigger.action.outTextForCoalition(coalition.side.BLUE, groupName .. " has been activated!", 20)
    return group
end
local function dumpEventInfo(event)
    local m = {}
    m[#m+1] = "Event ID: "
    m[#m+1] = event.id
    if event.initiator then 
        m[#m+1] = "\nInitiator : "
        m[#m+1] = event.initiator:getName()
    end
    if event.weapon then 
        m[#m+1] = "\nWeapon : "
        m[#m+1] = event.weapon :getTypeName()
    end 
    if event.target then 
        m[#m+1] = "\nTarget : "
        m[#m+1] = event.target :getName()
    end 
    trigger.action.outText(table.concat(m), 20)
end
local e = {}
function e:onEvent(event)
    local m = {}
    if event.id == world.event.S_EVENT_KILL then
        trigger.action.outText(event.target:getName() .. " Killed by (KILL EVENT )" .. event.initiator:getName(), 20)
        if allGroupsDead() then
            trigger.action.outTextForCoalition(coalition.side.BLUE, "All targets (Groups) have been destroyed!", 20)
        else
            local delay = math.random(1 * 60, 3 * 60)
            timer.scheduleFunction(activateGroup, {}, timer.getTime() + delay)
        end
    end
    --dumpEventInfo(event)
end
world.addEventHandler(e)
activateGroup()