They should be able to tell you what options they have for emergency system replacement. You also need to consider rerouting your telephone connections to your branches. If your building is uninhabitable and you need to relocate the main computer system, you will also need to relocate your telephone lines. Contact your phone company and ask them what emergency services are available. First, you should always be sure your backup media is stored off-site.
Many companies run their backup tapes overnight.
Be aware that by doing so, you are risking the loss of one day's data. If the building were to burn overnight, you would lose a day's business. With today's faster backup systems, you may want to rethink this process. In addition, if you do not make a full system backup nightly, be sure you have a copy of all programs and archive files stored off-site. Write all this information down and keep it somewhere safe.