This was a contest between 2 candidates. If the one, who won the majority of the Electoral College votes, is unfit to take office for whatever reason, you should logically go to the runner up of that election, who happened to win the majority of the popular vote. You can’t dismiss the vote of the people completely with a generic write-in.
The only other possibility I could think off, have a group of people run the business of the President for 2 years and set up elections 2018. This would force the GoP to get off their obstructionism path, it would force the DNC to recognize that, they as a party, have been rejected, and hopefully teach those politicians that they need to work together.
There are cities that can do that where party politics don’t matter much with republican mayors and liberal city councils. And if we haven’t learned one thing, that those political parties have overstayed their welcome, than it is “high time” to show them, GoP and DNC, in 2018 for good.