This shows how fragile the “National Popular Vote” compact would be. A state could easily back out of the deal. Even after the election, under suspicions of vote fraud, a state legislature could decide to award its electoral votes to the other candidate.
If I’m not mistaken, all of the states that have agreed to the ‘compact’ are controlled by democrats. Were a Republican to win the national popular vote, but not the traditional EC vote, you can take it to the bank that one or more of the states involved would quickly vote to change their law.
Regardless of the fact that the ‘compact’ violates the spirit of the Constitutional method of electing Presidents, consider that some/several democrat states (cough, cough, California) often take weeks to actually count their votes.