The company must determine how long they can be without the computer. Then you can start developing a plan.
For instance, If they can only be down for minutes, they you need to be replicating your data on another machine. If days, then you need to make sure you have access to another machine to load data from your backups.
What to do if machine is OK, but building is destroyed.
Etc. A disaster plan can takes a long period of time to develop.
Then you need to test it.
You will need to do plenty of research (or hire someone who is experienced in this to assist or do it for you)