I've had plenty of minor mistakes with the mouse with random armies. Usually you just have to take your loss and move on, adjust your strategy. It hurts when you accidentally make a move you did not intend.
But, I just had one though that pretty much doomed my 75 turn game, costing me a lvl. 10 hero . I was tired, but noticed it was my turn so in good sportsmanship played my turn before a long work shift so others would not have to wait. I somehow made a drastic mistake in moving a hero valkyrie and her army in enemy territory, the stack by itself was no doubt unstoppable and the strongest army in the game. But, somehow after the move I left her selected and moved her all alone in the forest, separated from her army next to a city of enemy elves! There was no way for her army to catch up to her.
I made my case with the opposition, but of course she was slaughtered and her leaderless army almost destroyed.
I wish there was a way to correct something like this. It was a great, exciting 75 turn game with 4 players left, and now I am bowing out due to a mis-click. Kind of stinks, I guess thats the game though.