DISCUSSIONS on “Rules for online games in HoMM3 and formulas for calculating player rating.”

There's no need to complicate the rules; if a player sees a chance and is reasonable, there's no need to interfere. After all, there's a possibility of winning. In the worst case, you can send the save file to a reputable player (from the AC, for example) with an agreement – if they say "no," the game is over. If you set a specific time limit, it will create an incentive to drag out a losing situation to a draw.
After all, this kind of question arises not just once a year.