'Slough' forming after mastopexy. Have I caused this? What is the treatment? How long will it take to heal?

Healing issues are more common with smokers and diabetics. It is not uncommon however after a reduction to have a separation at the lower aspect of the areola or the inverted T junction in the crease. This usually heals with minimal scarring over time. Be patient, work with your surgeon closely and things will work out.

Although difficult to give you accurate advice without viewing pictures, the types of superficial wound healing problems you describe do tend to heal over the course of a few weeks, usually without long-term sequelae. Sometimes, if the scars in these areas are wider, patients benefit from scar revision surgery down the line. Best wishes.