If a crash/disconnection occurs, the game must be played from the most accurately saved game (autosave usually) with movements being repeated the same as they were before the crash. If a crash is during a battle then the same applies for movements until a different bonus on a character alters the game significantly. From that point the game is considered new for the battle and the rest of the game is to be carried out as normal play.

Intentionally crashing or closing your game in order to replay a turn is cheating (for those who actually need it spelled out). This is true regardless of whether or not a player made a movement error and only wish to "fix" the problem. We all make errors and that is part of the game. You may not go back and "fix" them unless your opponent agrees to let you..