Why would you want such a dumb and stupid system you fool!
Simply do what all good RPGs do and disable the save/load system from functioning if only 1 human player is present. That way people like your map more, your map has a greater chance of being approved and no one can cheat. You can do this by counting the number of human players that are present and if they equal 1 then disabling the triggers that handle saving and loading.
bj_isSinglePlayer == true also does not stop cheating, as they could make a LAN game and hack them selves a hero of strong power by using a memory editor which is totally legal as they are not using it online.
Also implimenting a single player kick system is asking for your map to be ripped and ruined (people have a reason to do so) and that kind of trigger is insainly easy to edit and disable no matter how well you try and protect your map.