Just to add, if you are trekking, do not rely on an airline marketed travel insurance policy, many of these will not cover trekking over a specific altitude. I've never looked into credit card insurance exceptions, but I would be surprised if there weren't similar exceptions.

There are numerous stories of, shall we say less reputable, guiding outfits being very quick to call the helicopter in and then getting a "commission" from the helicopter company. I live in Singapore and have a blue chip health insurance including international travel, (which my job requires), but even they had quite a low altitude restriction.

There are specialist travel/sporting insurance companies that will cover you, but if during the purchasing process they don't specifically ask you to indicate altitude, review the list of excepted perils very carefully.