You have a job, a family, a life that will not pause, and a father who says he is fine by himself, thank you. This page will not hand you a test that settles it, because no such test exists. It will hand you something more useful: a way to decide window by window, and a way to make the windows you cannot avoid safer than they are today.
Before you answer him, notice what is rising in you, whether it is guilt about the hours you are at work or dread of the phone call you keep imagining. That is yours, it is normal, and it is worth one breath before the conversation starts.
Before you decide the disease has ended alone time, check the equipment, since a man who cannot hear the smoke alarm or the phone, or see the numbers on it, fails alone-time tests that a hearing aid and new glasses would pass for him.
When he says he is fine alone, he is defending something real, and it is not the empty house. Being alone is the last territory of full adulthood, and "I don't need a babysitter" usually means "I am afraid of what this concession starts." His certainty, though, is not evidence, since this disease damages the gauge a person uses to judge his own abilities, and the man most sure he is fine can be the one least able to say what he would do if the smoke alarm went off.
Which points at the real question. It was never "how bad is his memory." It is "what happens when something unexpected happens while no one is there." Walk the house with that question: the smoke alarm, the stove, the stranger at the door, the scam call, the night hours, the fall no one sees, and if there are guns in the home, where they are and how they are stored, because families never volunteer that one and an alone window is when it stops being theoretical. Ask him gently what he would do if the alarm went off, and write down the answer, but weigh what you have seen him do over anything he says, since a man can describe a fire plan he could not execute.
Then let go of the single verdict, because alone-safety is not one decision. Two hours in the afternoon is a different question from an evening, and an evening is a different question from a night, so rate each window in his real week honestly, cover the worst ones first, and let him keep the safest ones for now. Every one of those is a smaller argument than the one you have been having, and most of them he can still win. If you want one honest mirror for yourself, ask the question clinicians ask families: would you be comfortable leaving him alone for two days? Your stomach's answer is information.
Print the one-page log if you want somewhere to keep this, and take it to the appointment.
When the windows can no longer be covered, the memory care quick reference is the next page.
This is what the tracking is for. Ten dated entries from ten ordinary alone windows turn a fear into a pattern a doctor can act on.
He may never agree that the house has changed, and the windows can still get safer one at a time. The evaluation, the check-in call, and the Tuesday lunch cover the hours you cannot. You were never going to make the risk zero, only smaller than it is today.