Mealybugs did not destroy your tree - they don't chew on trees, just suck fluids. Photo #1 is a little too close and I can't really see it in your other photos but I suspect that's the graft. Your JM was top-grafted and part of the graft has failed. There's nothing you can do to revive the dead part but, with some effort, you can save and train what's left - it would be a multi-year effort. I had one break leaving only one branch. With patience and pruning, it turned into a nice tree but it took 15 years.
