Each enterprise is unique in its security and disaster strategy. The types of security and disaster events that may develop vary significantly from enterprise to enterprise. In my small company, terrorism threats are minimal. I have cell phones as backup for a major phone system outage, my data is backed up offsite, and PCs and servers are easily replaceable. However, the situation in your enterprise is most likely quite different from mine. To begin preparing your network for a disaster or the impact of a terrorist attack, specifically consider each step described above.
Start making explicit the threats to your network and the responses that mollify the impact of such threats.