lynn-a-roo,

No need to worry. Without minimizing the obvious risks involved in doing Everest, including the death zone, they are all in good hands, and I'm sure that safety is their #1 priority. Both Kurt and his group, as well as John's guide service (IMG), are experienced mountaineers, including multiple Everest summits. They've been there preparing and acclimating for this summit since late March, and I'm sure that, without rushing, they will spend as little time in the death zone as they have to in order to safely accomplish their goal, weather permitting, and then allow sufficient time for them all to enjoy the fruits of their labor on the summit. The death zone reference is limited to what the lack of oxygen at that altitude is gradually doing to your body if you're not using oxygen. Their use of oxygen throughout that time should hold off those ill effects until they get back down to a relatively safer elevation after they summit.

CaT

If future generations are to remember us with gratitude rather than contempt, we must leave them more than the miracle of technology. We must leave them a glimpse of the world as it was in the beginning, not just after we got through with it.
- Lyndon Johnson, on signing the Wilderness Act into law (1964)