Now that you mention that, I'm recalling that the inequality that you refer to is a changing thing.
The Constitution requires an enumeration of the population every 10 years. The Electoral College votes of each state constantly changes.
The National Popular Vote compact has no language that I saw that addresses what happens when compacting states reapportion such that they no longer comprise a majority of Electoral College votes.
To me, this would invalidate the entire effort so far, as states that already passed the compact would no longer have passed the bill that was presented, notwithstanding the language of "in substantially the same form." Exclusion of the impacts of apportionment is certainly "substantial."
Furthermore, the severability language "If any provision of this agreement is held invalid, the remaining provisions shall not be affected," will not apply in reverse to the instatiating provision of first attaining a compact of state comprising a majority of Electoral College votes, and then losing the justification for the initiating of the provisions in the first place.
You do have the provision "This agreement shall terminate if the electoral college is abolished." This could be revised to say that the agreement shall terminate also when the compact loses the majority of Electoral College votes, but that would make it a substantially different bill which would require it to be repassed in the Several States that already passed it.
Or... you can plan for the court challenges that would follow.
-PJ
You seem to have missed Article IV of the National Popular Vote bill. It simply says:
“This agreement shall take effect when states cumulatively possessing a majority of the electoral votes have enacted this agreement in substantially the same form and the enactments by such states have taken effect in each state.”
It would not be in effect if/when states do not possess a majority of electoral votes.