The situation: Player A has 1 life and several lifelink creatures adding up to 100 power. He swings at player B who has no defenders, planning to gain 100 life. Player B concedes. Without a valid defending player, player A can gain no life and has tapped all his creatures, and so player C can swing with a 2/2 and kill him.
Player A claims he can redirect his attack to player C after player B concedes.
Question: as per the official rules, can player A redirect his attack in response to player B conceding?
I already know the real answer is to play with sportsmanship in mind. In the specific example we were all having fun winding up player A, all done in good humour and would not be tolerated in a deliberately spiteful manner.
I was simply curious how the official rules would deal with it.