This chapter applies to all health care providers and other persons in relation to all health care agencies executed on and after July 1, 1990. This chapter supersedes all other provisions of law or parts thereof existing on July 1, 1990, to the extent such other provisions are inconsistent with the terms and operation of this chapter, provided that this chapter does not affect the provisions of law governing emergency health care. If the principal has a living will under Chapter 32 of this title, as now or hereafter amended, the living will shall not be operative so long as an agent is available who is authorized by a health care agency to deal with the subject of life-sustaining or death-delaying procedures for and on behalf of the principal. Furthermore, unless the health care agency provides otherwise, the agent who is known to the health care provider to be available and willing to make health care decisions for the patient has priority over any other person, including any guardian of the person, to act for the patient in all matters covered by the health care agency.