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.
My point is that the article you cite talks about when the compact initially takes effect.
There is no language regarding what happens after the compact takes effect but then no longer comprises states that make up a majority. The compact only addresses what happens when a state wishes to drop out of the compact, or when the Electoral College ceases to exist. Those are the only exit clauses that I see.
What happens if the compact takes effect, no states drop out and the Electoral College remains, but reapportionment reduces the compacting states back into a minority?
Does the compact remain in effect regardless, because once in effect it never terminates unless the Electoral College abolishes?
-PJ