States cannot opt out and have the law remain in place for next time.
The bill says:
“Any member state may withdraw from this agreement, except that a withdrawal occurring six months or less before the end of a Presidents term shall not become effective until a President or Vice President shall have been qualified to serve the next term.”
If a state withdrew, it would have to re-pass and re-enact the bill to have it be in effect for the next presidential election.