There should definitely be consequences for Milley. As you stated, it's not his job to assure his counterpart in Beijing that the US military will refuse to comply with what they perceive to be an order from an unbalanced CIC. If anyone is going to make that step it should be the Secretary of State.

Milley certainly has the right and obligation to refuse to obey a direct order he views as immoral. Along with that comes the willingness to accept whatever repercussions follow that refusal. What he did oversteps this responsibility and thus he must be held accountable.

This is yet another example of the continued erosion of Separation of Powers. At this rate the Constitution will become an anachronism in my lifetime. If it hasn't already.