I would extend it to "always required EXCEPT where contact with the co-authorizer was impossible within a timeframe that STRATCOM etc. thought was necessary given the circumstances." B/c rash retaliation is also undesirable in many real-world possible scenarios.
It's easy to stipulate that in a "we need a decision in the next 5 minutes" scenario, it could default to unitary authorization. I prefer that to a "if a nuke goes off against us, it defaults to unitary authorization" situation.
