No. The lower limbs are not likely to grow back. The weeping nature of the tree will allow the upper limbs to spread and hang down and should in time regain some of your privacy.

And get a new gardener.

I think you will probably get new branching of the trunk. All the African Sumacs around here are very bushy and seem to sprout all over. Many of our trees are willing to sprout from the trunk so just be patient.