Hang Seng Bank's vice-chairman and chief executive officer Louisa Cheang Wai-wan will take a three-month leave of absence as she recovers from a medical condition first disclosed last year, according to a statement by the lender. Margaret Kwan Wing Han, executive director and the head of Hang Seng's wealth and personal banking business, will serve as acting CEO during her absence, the bank said in a stock exchange filing.