My understanding is that an Afib related stroke is caused by a blood clot originating in the heart that travels to the brain. You may want to research whether there is a correlation between cholesterol and strokes?

There are two types of strokes, but both amount to the same thing: blocking of oxygenated blood supply to the affected area, so that area must die. If in the brain, it's potentially very bad. If in the heart, it's potentially very bad. If in the lungs, same thing.
The two kinds of stroke are from blockage due to stenosis (restriction of flow cross-section, which is what happens when there is plaque restricting flow too much) and due to clots that get jammed into place at a narrow-enough spot, and from there they prevent further flow of blood past that point. Anything needing that flow of blood will promptly die.
Once you have such a stenosis, that being caused by plaque deposition anywhere along a blood vessel, you can't reverse it. It can be displaced via a angioplasty, or pressed back out of the way, but it's usually just the buying of time. It can be bypassed with a stent of a length of blood vessel taken from somewhere else in your body, often an ankle.
Diet can only help so much if your genetics make you a hyperlipid producer. Some of us are that; we have hyperlipidemia and it's really not our fault any more than our looks or our big noses are. We have to choose our parents more carefully....next time.
So, no, in most cases, a diet cannot 'eliminate' the problem. It can help, though, by eating a diet suitable for the risks that genetics and other factors like stress make difficult to manage.