A couple of notes...
On recovering from a failure of all DCs: It can and does happen in a full virty environment. Particularly when you are single threaded on power, AC, storage, and networking as some of the infrastructures I support are.
One of the best things you can do to make this less traumatic is have a non-DC server carrying a secondary DNS zone (not AD Integrated) for the domain and for _msdcs.domain. Your PDC emu's network settings should use that server as a second or third DNS server for name resolution.
When a DC boots the first thing it does is look for DNS for its own domain. If it can't find DNS, it will keep retrying for 20 minutes before continuing the boot cycle. If all your DCs are down, and all your zones are AD Integrated, the first to boot obviously won't find DNS. The backup secondary zone speeds this process along. Saving you the horrible feeling of standing with users behind you trying to explain that "It'll be a little longer before you can continue doing your job; and no I can't make it go any faster."
Also, the default tombstone for domains built from 2003 SP2 on is 180 days, not 60.