Dealer's Tray is Short

Situation arose during my last session. Sharing the story because its lol funny and I also want to know if this would be standard procedure in other rooms.

Friday early night at a local 1/2 NL game

Dealers are switching and new dealer comes in and notices his tray is short 100 dollars. He immediately calls over the floor and lets him know. Dealer starts his round, after a hand or two a well-respected player states that he believes the previous dealer overpays a player in his previous down. He states player gave 200 in cash, and is given 300 in chips. Another player at the table says he also thinks he saw the same thing. Dealer calls floor over and tells floor. Floor leaves and asks the player who had at this point already moved to another game. Player denies he was over paid.

As this is all transpiring the dealer and other players at the table joke that maybe player x (at the same table, who also got change in the previous down, and who is awaiting a high hand payout) got the extra 100 when he rebought. Everyone jokes and laughs and says when the player gets his high hand payout that he'll owe the house 100 bucks. About 10 minutes go by, and floor comes over and says they need to go to the tapes.

The floor leaves, and after about 5 minutes, the manager of the room comes in and taps player x on the shoulder, they go about 20 feet from the table and player x, ends up having to give the manager 100 bucks from his wallet.

My questions;

1. I am assuming dealer who overpaid is getting a serious reprimand? Would this be a fireable offense?
2. Does the player have to pay the house? What would have happened if player had already gone bust, or refused?
3. How dumb does player X have to be to stay there - obviously waiting for his high hand payout but why not just come clean?!