According to an email blast (which you can also read here) from the Maine Green Independent Party, who worked hard to get that referendum on the ballot and passed, LD 1646 has passed both houses of the Legislature, bearing the title "An Act to Implement Ranked Choice Voting in 2021."
That title would seem to indicate that RCV will happen, although not in time for the next gubernatorial election as the voters had been led to believe. However, there is a multitude of tiny devils in the details.