The good news is that no one was hurt and no data was lost. News reports quote Brewster Kahle as saying, "Luckily, we're not aware of the loss of any collections."
The fire is not believed to have caused major disruption to the website. While inconvenient, the fire was only at the organization's offices. All the terabytes of data are stored in server facilities some miles away. I also suspect the Internet Archive also has off-site backups, as any large data archive will always have.
The Internet Archive web site at https://blog.archive.org/2013/11/06/scanning-center-fire-please-help-rebuild/ says, "This episode has reminded us that digitizing and making copies are good strategies for both access and preservation. We have copies of the data in the Internet Archive in multiple locations, so even if our main building had been involved in the fire we still would not have lost the amazing content we have all worked so hard to collect..."