GlueBall
Mt Everest isn't the problem here, none of the airways I know of in that area route over the big one. However the whole Tibetan plateau is (a) bleedin big and (b) bleedin high. If you have a decompression in that area it will take you a considerable period of time to reach an area where the MSAs allow you to descend to 14k or less, hence the comments from others about sopplementary Oxygen on some routes.