This happened to my niece. She's a basically healthy person who rarely needs to see a doctor, so she doesn't go often.
Her doctor also treated my mother (who passed away just shy of 95) for about 16 years. The doctor frequently complained that rules and regulations and administrative and governmental changes were very disheartening and had him thinking of quitting his practice.
One thing in particular was the rise of hospitalists - a hospital can decide that ALL of its inpatients WILL be treated, while in the hospital, by a doctor paid by the hospital to manage their inpatients. The patient's regular doctor cannot treat them while they are hospitalized, only the hospitalist - a complete stranger who knows diddly about them. If that had been in effect during his care of my mother, she would have died 10 years before she did.
My mother went into a nursing home 2 yrs before she died, and as most people know, the nursing home usually has its own doctor, period (at least, for medicaid patients).
So, my niece lost track of the doctor. Last year she had to go to the ER with a kidney stone. When they asked her who her doctor was and she told them, she was informed that he'd closed his practice months before. A new doctor was in his office space, but she was told that "no one knew" where patients' records were. She had never gotten any notification.
She never pursued it, but I know that legally those records MUST be available somewhere, or lawsuits would be filed.
I think the doctor just said **** it one day and walked out. He doesn't have to worry about any state medical body because he retired - he isn't going to practice medicine again.
Life without Mexican food is no life at all