X почил в бозе - X joined (met, went to meet) his Maker
X went the way of all flesh.
«Но не доехав до места назначения, папаша мой не выдержал обиды своего должностного понижения и почил, как говорится, в Бозе в номере парижской гостиницы...» (Максимов 2). "Before he reached his destination, however, my papa was unable to endure the affront of his political demotion, and he joined his Maker, as they say, in a Paris hotelroom..." (2a).