They can sue but the question is who. The health insurance companies are strongly protected by ERISA which prohibits any compensation apart from the financial cost of the denied treatment (excluding cost of any medical complications resulting from the denied treatment and null and void if the patient dies first).
They will sue the doctors, claiming that if they coded the case differently or used some other form, the drug would be paid for.
When you get a drug for a patient that insurance doesn’t want to pay for, each hoop you have to jump through is smaller than the last one. That is to say, after each “no”, the next one up the line takes more time to contact, a longer explanation or more forms, until eventually (if they don’t give up) the time involved becomes unsupportable.
That’s for one patient. Two patients, three, five? Impossible.
But, the insurance company always has the out of saying, “The doctor did not follow our (impossible) procedure”.