Generally there would be no potential medical malpractice liability if a patient declines a medical procedure. That happens all the time.
Physicians can fire patients, although they seldom do so because of declining a medical procedure. Professional ethics and state laws generally require the physician to first hand off the patient to another physician first; they can't just drop someone with zero notice.
There is generally no mandated checklist, at least not from a legal standpoint. Some healthcare provider organizations do require their employees to follow certain written standards of care. Medical societies also publish evidence-based care guidelines. Compliance is voluntary but gross deviations could be factor in liability cases or in actions by state medical boards.
Insurance reimbursement is an entirely separate issue. Every insurance plan has a different network of providers and different rules about which services are covered under various circumstances.