Panel Page with Node Views, Flags and Rules Integration
If you can create a view (using the Views module) of those users that correspond to all those "prospects who did not get accepted" for a given game node, then you can process the results of a VBO enabled view via Rules, using a rule that looks like so:


Rules Event: After flagging the prospects flag with an accept flag (flag B).
Rules Actions:


Load the VBO list of the users in your View.
Add a loop to perform a Rules Action "Send an eMail", for each user contained in your Views results.



For more details, have a look at the tutorial "How to process the results of a VBO enabled view via Rules?".