So very sorry for your loss, Richard.
I hope that people will pay attention to your plea to prepare their advance directives. In most states in the US you can find free valid health care directive forms (sometimes called Durable Powers of Attorney for Health Care) online and fill them out. Make sure that they are completed with all legal requirements–usually that means they must be PRINTED OUT, and signed before a notary public or witnesses.
Your doctor or local hospital may also have resources to help you prepare your directive. I teach a two hour class on Advance Health Care Directives to the general public in California at a local hospital. I teach this class with a social worker, and we are able to answer questions about the medical and legal aspects of the form. Our participants almost universally tell us how valuable this is.