More than 700 of OpenAI’s 770 employees threatened to leave the startup if the company’s entire board of directors does not step down, seething over the ouster of former CEO Sam Altman. The employees, writing in an open letter, said they’d join Altman at his new post at Microsoft — adding yet another twist to the three-day saga that has rocked the tech world. Competitors, smelling blood in the water, are already trying to poach OpenAI’s engineers.