Who cares?
I care because there's an appalling lack of rigour going around and it's not helpful.
1. Does the network still provide strong double-spend protection?
2. Can users freely* publish valid transactions to the Blockchain (censorship resistance)?
*That is, subject only to marginal transaction fees.
I think that's a good start. The question can then be translated to "what are the minimum requirements needed to prevent double spending and censorship?"
I suspect the answer in terms of the number of world-wide copies of the blockchain needed has a lower bound of 1, depending on our ability to create efficient fraud proofs and to implement better privacy behaviour in wallets.
With single node or 6 nodes we do not need POW. We already had this centralized services. ... but they are all down.