This is what the expression "crunch time" was invented for. We say... if the buyer has the cash (and that's not inconceivable considering the kind of investor who was eyeing up flip possibilities when the Pan Pensinsula project was launched)... go ahead, finish the deal, live in it or get a tenant, and wait. You've only lost money if you sell at or near the bottom.
"Several months ahead of schedule", though... interesting, isn't it, how falling prices can focus a developer's mind?