With single node or 6 nodes we do not need POW. We already had this centralized services. ... but they are all down.
Can you rephrase your comment in terms of how the number of nodes is related to the number of copies of the blockchain in the world, and how both of those affect the ability of an attacker to perform double spending and censorship attacks?
If there is only 1 copy of blockchain then I expect it is located in 1 datacenter. (node)