I Had an Eyebrow Transplant and Much of the Hair That Was There Fell Out. What Should I Do?

I am sure that this possibility was discussed in your informed consent document, and it should have been discussed with by your doctor. If it does not come back in 12 months or so after the eyebrow transplant, I would assume that it is lost. If I were your surgeon, I would bring you back to surgery and make it right with you at no charge, as I always attend to complications that occur as part of any surgery I do.