Now that html 5 is stable I think its high time we implement auto save/ajax functionality. No more disconnecting with 3 seconds to go losing the whole turn. All moves should be auto saved by default. So if you make lot of moves in 3.5 minutes and disconnect all your moves should be saved and you shouldn't have to redo any move.
If for some reason you want to reset a turn there should be a separate button at the top left corner of the screen saying "Reset turn " . Clicking on it should prompt you whether you are sure asking something like "Are you sure you want to reset turn ?". When you reset turn all auto saved changes get cancelled which is the current functionality when you disconnect without ending turn.
I think this has been proposed before but it should be implemented now. I think this will immensely help all the 20 people games and scenarios where the server load is highest and people are most likely disconnect often.