The only mulberry I grow here is Illlinois Everbearing and it too has a mysterious tendency to check out with no suicide note. Sometimes they get canker that I've never identified that kills the trees in a few years and sometimes they just don't come out of winter. At least they often send up suckers from the roots when this happens so you can graft a new tree. They are susceptible to scale so oil may be in order.
They are impossible for me to keep in a small space but you can keep them in-bounds by pruning them to a weep and summer pruning them once a season- removing all vigorous upright growth. They make beautiful trees managed this way and you keep a lot of fruit in ladderless reach.