I thought a number of states have “Sore-Loser” laws..meaning, if you run in a party primary and lose, you can’t run as an independent in the general election..I may be wrong..
But those laws are not superior to a State Legislature's plenary authority to appoint electors in whatever manner they choose.
I have been predicting a four-way race in 2016 since November 2012, because neither party is capable of unifying under a single candidate any longer.
The way I see it now, Trump will be the Republican nominee and Biden/Warren the Democrat ticket. Hillary and Jeb will run together on some type of Bell-Everett platform (keep everything the way it is and don't bother about the details), and there may very well be some sort of trucon/socon candidate as well.