How long is his leave for? Is this a paid leave? Perhaps he originally was not planning on taking any time off and now something has changed? Would he have been passed over for a project that he wanted had he told anyone? How would you have juggled things had he fallen down a flight of stairs and broken his leg, necessitating that he be out for an even longer period of time? How is how he handles his personal life, any of your business whatsoever?