You don't vote for Hillary or Trump.
You vote for the electors representing your state.
Some states have laws against "faithless electors", but I'll bet they have a "out" for a ticket that no longer exists.
Here's an example from Minnesota:
https://www.revisor.leg.state.mn.us/statutes/?id=208.08&year=2008
The invalidation of an elector's vote or abstention on the ballot for president or vice president does not apply if the presidential candidate under whose party's name the elector was chosen has without condition released the elector or has died or become mentally disabled.
This doesn't give an out for withdrawal from the ticket. But, all it takes is a declaration of Clinton's "mental disability".
If they do go down this route, Clinton will be declared unfit or ineligible for office, mentally disabled, or even clinically dead if it's necessary to assign her electoral votes to someone else.
In Democrat states in particular, you can take this to the bank: a judge will make whatever ruling is necessary to award the electoral votes to the Democrat replacement.
“In Democrat states in particular, you can take this to the bank: a judge will make whatever ruling is necessary to award the electoral votes to the Democrat replacement.”
While that is certainly true, the RAT States are in the MINORITY today.