OPENING Swiss watchmaker Audemars Piguet is opening a boutique in East Hampton, N.Y. Day-to-day operations will be overseen by New York City retailer Material Good. (Above) Millenary Hand-Wound with 0.6 ct. t.w. diamonds in 18k white gold case and bracelet; $47,000; Audemars Piguet; 212-758-8400; audemarspiguet.com  COMINGS AND GOINGS Ippolita Rostagno has bought back a majority stake in her namesake brand, Ippolita, from private equity firm ­Castanea Partners. Rostagno will become CEO, replacing Jill Beraud, and retain her ­position as chief creative officer. Minority investors include friends and family. In addition, the company has hired Diego McDonald, the president of Ghurka, as chief financial officer; brand veteran Beth Fazio as creative director; Ghurka alum Justin Sellman as head