I found this white paper from the early days of XenServer. I think it’s worth a once over as most of the information and logic remain valid. The flow chart of recovery steps makes it look pretty simple and can maybe help someone out of a jam. This is definitely something you want in your disaster recovery plan!
XenServer System Recovery Guide
Orignal source: http://support.citrix.com/servlet/KbServlet/download/17140-102-671536/XenServer%20System%20Recovery%20Guide.pdf