I actually had this happen once. Tournament was down to 3 players, all 3 were in the money. Fire alarm went off. Voice comes over PA saying "please exit the casino." There was a hand in process. I walked to the table, told players "no more betting on this hand," instructed dealer to run board out and award pot to best hand. I then instructed players to leave their chips on the table and exit the building. There actually was a fire on one of the upper floors and it took 3 hours before the building was able to be reoccupied.
I fully expected that the players had left, so I had already planned on forcing an even chop and bagging their money for pick up later but the 3 guys were all still there and wanted to resume play. Employees were put in another area outside than our guests so I had no idea that they would have stuck around.
I don't really have any advice on the matter, just felt like sharing my story, lol.