Dealing with EventListeners and preventing memory leaks

Help
1

I have been using EventListeners a lot, and when I added one that listens for roundEnd broadcast to a weapon, it was still called even after the weapon is destroyed.
Looking through the Core API documentation for event listener, there is one example.
I feel that it raises more questions.

function OnResourceChanged(player, resName, resValue)
    print("Resource " .. resName .. " = " .. resValue)
end

local resourceChangedListener = nil

function OnPlayerJoined(player)
    if player == Game.GetLocalPlayer() then
        resourceChangedListener = player.resourceChangedEvent:Connect(OnResourceChanged)
    end
end

if Game.GetLocalPlayer() then
    OnPlayerJoined(Game.GetLocalPlayer())
else
    Game.playerJoinedEvent:Connect(OnPlayerJoined)
end

function OnDestroyed(obj)
    if resourceChangedListener and resourceChangedListener.isConnected then
        resourceChangedListener:Disconnect()
        resourceChangedListener = nil
    end
end

script.destroyEvent:Connect(OnDestroyed)

From what I can see so far, memory leaks happen when broadcaster is still there, but the script containing the listener is destroyed.

  1. Is the reference to the listener kept by the broadcaster keeping the listener from getting garbage colllected?
  2. Are we setting the variable holding the listener to nil because this is still a reference that prevents garbage collection? Does this not get freed automatically when the script is destroyed and the variable goes out of scope?
  3. What about for the opposite direction of a more permanent script listening to broadcast of a transient object? When the object is deleted and this listener disconnected, would the listener be garbage collected if we never saved it to a variable?
  4. In terms of a very commonly used function, Game.playerJoinedEvent, why do the client script never disconnect this listener? When the player leaves wouldn't this listener be left there?
  5. What about the existence of a onDestroy listener itself? Presumably this is a script that exists longer than the object. Should this listener also be disconnected and set to nil when it is executed?
  6. Is there any big downsides (outside of maybe performance) to not just have script:OnDestroyed listener for everything?

Thanks.