Ok , how about this..
Get the auto-sav feature to save every 1 minute. 5 sav files overwriting...
Then something in the game, thats constantly checking that players are sync , maybe every 20 seconds.
Then if the game detects a desync , a message pops up saying
"de-sync has happen , Re-Host from Savegame250.sav etc"
Every player then has to click okay to acknowledge it which then returns them all to lobby to rehost. At worse you only lose a minute of play