My BIL had like 26 full cords of walnut in his basement, those beetles had a lot of fun down there lol.Yes the sapwood goes quick. Usually gets the damn Powder Post Beetles. But the heartwood is solid for years. Just my experience.
I imagine the sapwood would go first, but I've seen the rest of it go pretty quick too.
I have a black locust log on the ground I've been using since last fall as dunnage for other logs, it's got water spouts on it lol.