What would you do?

We had reached an impasse between 4 of us in a World 2.0 game. I own North America and South America (except for NE Brazil). Player 2 owns Africa and is my opponent in NE Brazil. Players 3 and 4 hold most of Asia and Oceania, respectively.
Player 2 offers a Non-Aggression pact in Brazil in exchange we'd combine our forces and attack Player 3.
Before Player 2's turn, Player 4 is able to gain a foothold in Africa - denying Player 2 important armies. Player 2 could easily regain Africa and start on our quest.
BUT------
He announces, then proceeds to screw up and place all his armies in the wrong location, where he can't regain Africa or pretty much do any attacking.
I see this, know it is probably a mistake, but I agree. I seriously considered hanging him out to dry.
What would you have done??????
Player 2 offers a Non-Aggression pact in Brazil in exchange we'd combine our forces and attack Player 3.
Before Player 2's turn, Player 4 is able to gain a foothold in Africa - denying Player 2 important armies. Player 2 could easily regain Africa and start on our quest.
BUT------
He announces, then proceeds to screw up and place all his armies in the wrong location, where he can't regain Africa or pretty much do any attacking.
I see this, know it is probably a mistake, but I agree. I seriously considered hanging him out to dry.
What would you have done??????