What I understood: Michael agrees to deposit 600 million in the Vatican bank. In exchange he is supposed to get the control of the majority of Immobiliare. The deal fails when the Pope is getting sick and unable to sign the deal.
HARRISON: What if he dies?
KEINSZIG: Then, as you Americans say, all bets are off.
Later, Michael says to Keinszig: "I understand. Your tactics are despicable."

This is where I get lost:
1) What kind of tactics is Michael talking about? As far as I understand, Keinszig argues that only a new pope can sign the deal.

2) Does Michael lose any money? He can withdraw the money from the Vatican Bank, can't he?

And all the rest: The role of Lamberto, the disappearing of Keinszig after Lamberto becomes the new Pope, are a mystery to me.