I was on a trans-atlantic flight one time when a pax passed away. It happened during the night, and I caught a lot of the drama as they tried to save him (her?). A couple of the FA's were pretty broken up and distraught (understandable). Most of the other pax were sleeping and never even noticed anything going on. The body was in one of the seats that border on the open area near a flight attendent station. They covered the body with blankets, and it was kind of curled up in the corner and I don't think most people on board even noticed it as they walked past to deplane at the end of the flight.

Sad thing to witness.