If a provider leaves your practice, you can delete that provider from your Hint account. You are then given the choice to remove the provider assignment from existing patients or to reassign patients to a new provider.
Here's how:
Go to Admin > Providers & Patients
Click 'Delete' next to the provider's name
You can now choose to remove provider assignment from her patients, or as seen below, select a new provider to assign to her patients
Click 'Delete'