What lightman has said is absolutely correct. However, if they join NALC without leaving the ELCA, the ELCA would probably kick them out, and the congregation keeps their property.
Correct: The ELCA forbids “dual rostering” and the Constitutions state the congregations expelled for any infraction keep their property.
That can become the backup plan for congregations where more than 50% would like to leave but the votes fall short of 2/3.