Hi,
I would disembark an entire B747 or A380.
Nobody can say for sure that the area has been checked again and everything is OK. None Crew Member.
And, in flight: If I had a passenger shouting the following: "WE ARE GOING TO DIE" then, I would land in an alternate aerodrome. Unless, my Cabin Crew could say for sure that they talk to that passenger and it was an insanity person, which should be writen in a medical paper obviously.
B.R