Hello,
This has been moved to the vCenter server forum.
If SSO is down and all you use is SSO for vCenter, then you will not be able to login. Actually, since SSO is used for nearly everything between VMware products such as vCenter, Location Services, VIN, etc. It is a good machine to have backed up and available. Local to the machine users can always login to vCenter if you have given them permission, so if SSO goes away, you can still access vCenter.
Best regards,
Edward L. Haletky
VMware Communities User Moderator, VMware vExpert 2009, 2010, 2011,2012,2013,2014
Author of the books 'VMWare ESX and ESXi in the Enterprise: Planning Deployment Virtualization Servers', Copyright 2011 Pearson Education. 'VMware vSphere and Virtual Infrastructure Security: Securing the Virtual Environment', Copyright 2009 Pearson Education.
Virtualization and Cloud Security Analyst: The Virtualization Practice, LLC -- vSphere Upgrade Saga -- Virtualization Security Round Table Podcast