Similarly, Equitable Life may have sopped up a lot of excess space at 1290 Avenue of the Americas, but it is leaving a huge chunk of emptiness at 787 Seventh Ave ., the headquarters it built for itself just 10 years ago . ( At least part of that chunk will soon be filled : Willkie Farr & AMP; Gallagher, the law firm that jumped into the news when former New York Gov . Mario Cuomo joined it earlier this year, is moving in .)