Does a successor trustee have to notify creditors that the trustor died? How does the successor trustee do this?

It depends on the debts, the assets, and the beneficiaries.  Yes, you can negotiate a lower pay-off of the debts.  However, if there are unpaid debts, the trustee may be personally liable and the beneficiaries may take their inheritance subject to the decedent's debts. There is a trust claims procedure with the probate court.  Best thing to do is hire an attorney for trust administration.