If I have Platinum Angel in play, and I play Final Fortune and do NOT win game within next round, what happens then?
Do I lose the game?
And if I do not, will the spell "stay in play" so that the second my Platinum Angel leaves play (like fx. 3 rounds later), I lose game?
Final Fortune sets up a delayed trigger wherein you loose the game at the end of thnext turn. Since Platinum Angel says that you can't loose, the trigger resolves but fails to make you loose. The trigger is now gone, so you're good.