There really isn't much you can do. Patients have autonomy and they'll make their own decisions. You need to document the conversation you had with presented treatment (and choosing nothing is an option), then you need to tell the patient exactly what happens with every choice. Usually with a patient like yours, I'll explain pain, infection, and possibility of death. But it's important to communicate the risks/benefits to any procedure.
ie - decay to pulp (you need RCT/bu/PFM - $$$, but you keep your tooth, or extraction - cheap, but no more tooth, or doing nothing - super cheap, but risk of pain/infection and possible death). But sadly, this conversation does a little better in private practice over dental school.