A health care power of attorney agent makes decisions according to your values. If a situation were to arise in which they were unsure of what you'd want, they should make decisions based on what they (and the doctors) believe is in your best interest.
No. While health care decisions could have a financial impact, a health care power of attorney agent DOES NOT make financial decisions.
In contrast to a health care power of attorney, which takes effect any time you're unable to make medical decisions for yourself, a living will is specifically about the type of care you do or do not want to receive if you were to become permanently unconscious or terminally ill and unable to communicate.
You may want to execute a living will because then your end-of-life wishes are written down on paper. However, they don't give your surrogate decision-maker as much flexibility to make decisions, which may be unfortunate if you forget to update your living will even as your wishes and values change.
Unfortunately, no. Sometimes it's not possible to honor your wishes. For example, you might prefer to spend your last days at home, but your condition may make that impossible.
A health care power of attorney agent only has the authority to make medical decisions when a doctor deems you unable to make them for yourself. If you were to regain the capacity to make medical decisions, then you'd also regain the authority to make your own medical decisions.
Yes. If you decide to appoint someone else or decide to have no health care power of attorney agent at all, notify the agent, your doctor, and whoever else you told. You should also destroy the original health care power of attorney and all its copies.
Their authority ends upon your death, unless you revoke your health care power of attorney while you're alive, in which case their authority would end whenever you revoke your health care power of attorney.