Travel insurance is mandatory to have to join an adventurous trip in the Himalayas. It is for your safety. The travel insurance must cover things like illness, medical emergencies, accidents, death, trip cancellation, and loss of personal baggage & items. All costs for Emergency Evacuation must be paid in cash in Nepal unless an insurance company has agreed to pay all the cost on your behalf. Make sure that your travel insurance covers activities in the Himalayas if you are participating in them.
*Note: Foreigners are not allowed to purchase an insurance policy in Nepal. So make sure to purchase good travel insurance in your country, and it is your responsibility to check whether your insurance policy is adequate or not.