Here's another pic of the entire tree.

Unless you do some bridge-grafting or inarch grafting, everything above the girdled area will die. Sure, it looks good now, but it won't last.
I see it's already pushing new growth below the girdled area - if that's above the graft union, you can allow those shoots to grow, select the most vigorous, prune off the damaged trunk and be back to a similar stature within 2-3 years.

I guess my question is: why is it acting normal now when there's no flow of xylem or phloem? Is it left over nutrients in the above girdled area that's making it act normal now? And how long before I start to see it dye off? Have there been reports of trees healing over a girdled area? Grabbing at straws I know but curious non the less.
I would consider grafting but I don't have any dormant wood left.

It is surviving primarily off stored nutrition in the tissues above the damage. There is still some flow as well in the sap wood that is below the cambium, but that tissue while still alive is incapable of cell division and growth.... so it's clock is ticking.

I have seen some apples rebound after an incredible amount of bark cambium loss (horse pasture), but there was always some continuous cambium. I don't think any tree will recover from total girdling.

Agree, all the way downhill from here,.. unless there is just a little strip of bark not chewed down all the way to the wood, that might be the case on the opposite side of picture showing a slight hint.