Two years after Sabato de Sarno was appointed to take the creative reins at a flagging Gucci, his efforts to revive consumer demand for the Italian megabrand have run out of road. The company announced his departure Thursday, just days before owner Kering is set to report its annual results. Gucci, Kering’s biggest and most profitable brand, has been in a sustained slump, with revenue down 26 percent year-on-year in the third quarter.