Most insurers still haven’t wrapped their brains around outdoor sports—especially those that entail some degree of risk, like mountain climbing. Typical health insurance policies won’t cover an expensive evacuation from a wilderness setting in the event of an injury that’s immobilizing or life threatening. Unless you get travel insurance that specifically covers circumstances that could slam the door on your trip—such as weather preventing you from getting to your destination—you’ll eat the entire cost.
The best solution I’ve seen is the Adventure Travel Protection Plan from AIG/Travel Guard (travelguard.com), one of the only policies that covers climbing and hiking at altitude. The basic plan provides a menu of coverage including trip cancellation or interruption, reimbursement for costs of replacing gear if baggage is lost, and up to $25,000 for emergency medical expenses and $500,000 for emergency evacuation. There are optional additions to the coverage, too, including for cancelling your trip for any reason.
Most travel insurance plans exclude certain hazardous sports activities. This can include mountaineering, bungee jumping, hang gliding, snorkeling or other activities. Some plans do not exclude these items and others will waive the exclusions if an upgrade is purchased. Always refer to the certificate of insurance for details.