Have you had any progress on this issue?
Another way that might work is to close the game from MonoTouch:
game.Exit();
As a simple test, you can make a timer in MonoTouch, which does it after, for example. 5 seconds. If this works, you will need to find a way for MonoGame to communicate with MonoTouch to let you know when the game should be stopped. This is not ideal, but if nothing worked, this might be your only option.
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