Notify when a reserve player is promoted
When someone leaves a session that has reserve players, and one of the reserves is promoted to a session player, a notification should be sent to that person, and perhaps also to the game creator. Often, this promotion happens right before the game starts, and that can catch the session creator and reserve player by surprise.
Whirled Peas commented
While you're looking into this, there are also instances when I was automatically promoted from reserves and didn't want to be. I joined as reserve because I wasn't sure I'd be available. I'd like an option to "not auto-promote"