Last Minute Property Law Panic

Aur kya karun? I'm three days away from the exam and still, I'm stuck on this one thing in TPA - what happens when a contractual obligation is destroyed by an irresistible supervening event, but the party was aware of the possibility of such an event? Do we apply the doctrine of frustration or is it a case of impossibility? Sab kuch jaanta hoon, par agar ek question aa jaye toh kuch nahi pata. Frustration se related sab topics to pass karte hain, par is case mein confusion hai. Kya yeh impossibility ka case hai? Ya frustration se to kuch alag hoga? Kya karein, kya padein - kuch nahi pata.