I would guess the legislators would then write a constitutional amendment to better bind future electors.
Two states have already made votes that don't align with the popular vote void. The National Popular Vote project notes:
In a 1919 case involving a state statute entitled “An act granting to women the right to vote for presidential electors,” the Maine Supreme Judicial Court wrote (In re Opinion of the Justices):
“[E]ach state is thereby clothed with the absolute power to appoint electors in such manner as it may see fit, without any interference or control on the part of the federal government, except, of course, in case of attempted discrimination as to race, color, or previous condition of servitude….”
So a state could simply assign a backup elector in that case. So fifty state laws could substitute for one federal constitutional amendment.
It might be difficult to pass such an amendment, as that scenario so clearly favors the Democrats. A constitutional amendment requires bipartisan support.
I didn't find any useful information about Alabama electors, but according to the Bustle link that @luweiqi posted:
But we could see some such electors in 2016; two Republican electors, one from Georgia and one from Texas — states that don't have laws requiring faithfulness — have suggested they may withhold their electoral votes from Trump should he win in those states.
But that wouldn't necessarily impact the election. They are talking about "withholding" their vote from Donald Trump. Unless they vote for Hillary Clinton, that can only send the election to Congress. It takes a majority of all possible votes to win the election. If Clinton doesn't have it, removing votes from Trump doesn't give it to her. She'd have to add votes to her total.
Republicans aren't terribly happy with Trump, but they don't like Clinton either. Faithless electors are more likely to vote for Pence or similar than to vote for Clinton. Republicans will almost certainly control enough House delegations to keep Clinton from winning there (assuming an electoral college deadlock) due to their dominance in small states like Wyoming and the Dakotas.
The House might just vote Trump. If there are enough Never Trump Republicans to deadlock the House though, the presidency could go to the new vice-president. If there is no vice-president (because neither candidate gets the necessary 51 Senate votes), the presidency goes to the Speaker of the House.
So faithless electors are unlikely to elect Clinton. It's barely possible that they could cause Tim Kaine to be elected, although House Republicans might manage to rally behind Trump and prevent that. There is a much higher chance of Mike Pence and an odd corner case where it goes to Paul Ryan or whomever is the next Speaker of the House.
Now, if Clinton had a faithless elector, that could switch the election to Trump or another Republican.