Assumptions are the foundation upon which failure can occur. As part of the DR plan every assumption needs to be questioned:
To what environment would recovery occur?
Can we gain access to our DR site in the event of a disaster?
Will key staff be reachable in the event of a disaster?
Will key staff be able to commute in the event of a disaster?
Will internet access be available to key staff during a disaster?
If a disaster is widespread, will many companies converge onto and overwhelm the planned DR site?
Deploying or retracting a web part that is only loaded on a single page can cause catastrophic failure. One example of when this can occur is when trying to perform a retract via the Central Administration user interface of a SharePoint solution that is deployed to Central Administration itself. For any such solution, Central Administration happily tries to retract the solution and it fails. The author ran into this when trying to uninstall Powerpivotwebapp.wsp. The solution was to perform the retract via PowerShell. During several initial retract attempts, the Central Administration in production was rendered inaccessible. All attempts to repair Central Administration failed. Luckily, rollback was possible.