What happens for authentication if single DC at the site goes down?

200 Users
Two AD Sites

Two DCs at the main site - "A" , one DC at the second site "B"

At site A:
We will have a main Exchange 2010 server and two DCs / GCs - Outlook will be running in cache mode.
Some application servers.

At site B:
A single DC and some servers.

Q)
If the single DC at site "B" goes down, will the PCs at site "B" still authenticate across the WAN ?

I would like if you could point a MS document which states the expected behavior.
If you have have other notes, please add.

I am aware machines would need a valid DNS server, also that I would expect Outlook clients to continue to function as cached mode they should be using a copy of the offline address book rather then sending queries to the GC.

Thanks.