If K*rry were to win, there's nothing preventing his electors from voting for H*ll*ry in the Electoral College.
I don't think it even has to be that difficult. If she decides she wants to run, a gazillion liberal lawyers are going to challenge every state law to get her on the ballot.
There's no way they won't be successful in "giving the people a choice" (Puke!) and Bingo!, she's on, and good to go.