A health care power of attorney makes decisions according to your values. If a situation were to arise in which I'm unsure of what you'd want, I'd make decisions based on what I (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 DOES NOT make financial decisions. 

Living wills are useful because your general wishes are written down on paper; however, they're sometimes inadequate to give guidance on the various medical scenarios that patients encounter. So the benefit of having a health care power of attorney is that you have someone who's able to navigate the issue as you would. 

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 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 at all, notify me, your doctor, and whoever else you told. It'd also be a good idea to destroy the original health care power of attorney form and all its copies.