I never had this problem to be honest. I think your stats will registrer as they were when last !ff came. No more kills or creeps. And of course, winner is the other team that did not ff. It is clear to me (logic) that the stats get registered when the game end, not earlier - replay must be readable to be parsed by the server. When they got registered, site must sync with bots. This probably doesn't happen continuously, but each 5 or 10 minutes.
Maybe the problem can occur when you leave the game after !ff, enter new game, the new game start and then the !ffed game ended. Maybe then there can be this bug?