I'm a rookie, no idea how big a 4y old tree's roots are. I would be afraid to dig it up and pot it, afraid that I would harm the already-damaged roots. I think the roots had to have been damaged for it to take this long to push out leaves. If you have some creative better way to insulate it this winter and keep the roots from freezing, would it do OK? Of course, the question is 'do you plan to keep it in the ground long term' ?
Good luck with this one, Matt, I'd like to hear what you do with it and how it does in the future.