Well, I see multiple things to discuss here.
Considering Player B's hand has not been killed (cards have been identified) and have been faced up (no matter how), the hand should be live.
Sidestory
I know a situation happened in Paris in February on a cash game table.
(Uncommon betting pattern from the beginning of the hand)
River
Player C bet
Player D call
C show
(now timestretch Matrix mode)
D throw his cards face down towards the dealer who just removed the cut card from the bottom of the deck and throw it on the table.
D cards and cut card collide in the air, D cards turn face up on the table... He has the NUTS !
Pot was awarded to B
Yes, the dealer made a wrong call by facing up the cards, but to me (and I know we all are not on the same page on this) you can't alter a judgement just because your staff made a mistake. If you do, that means you are doing some kind of commercial gesture (like offering a drink to a customer who got pushed by a waiter) and on a tournament we must stick close to 100% equity no matter what.
Also, I really should have ask to the dealer once he got out from the table, what he was thinking about, not to have an argument but to understand if he got confused, or it was a deliberate call.
Anyway great case, thank you !