We each take single player turns of the same game. when you've reached the start of a new season and you see the message pause the game, save, and quit. Go to the save games folder and upload the folder as an attachment I guess.
If the fort fails on your turn, you are free to get the last uploaded save to start again. However if it proves to be a stalemate (as in none of us can overcome the current failure) the game will finish.