Talk to an estate attorney and they can give you some advice, but ultimately you'll never be able to account for every possibility, and you're going to have to trust somebody to make the right decisions for you at some point.
Anecdotally, a family friend was barely clinging on to life for a couple weeks enduring heavy pain meds and abject misery. Only when his close friend, and executor of his estate, sat beside him and told him everything was going to be alright did he finally find peace and let go. He was gone within 30 minutes.
