Which major US life insurance companies sell valid life insurance policies to US citizens currently residing in the Cayman Islands?

To the best of my knowledge and belief no US life insurance company will issue a policy to a US citizen or any one else in the Cayman Islands unless they are licensed to do business in that domain. The Cayman Islands are not US territory. If you already have the policy, however, and you choose to go to these islands to live they cannot take the policy away from you.

The reason for this is that life insurance company find it difficult to complete "inspection reports" outside of US territory. They need to confirm that the answers given on the application are true to the best of the applicants belief.

Sagicor Life Insurance Company is an American company which has a base in Cayman Islands. I believe AllState and PanAmerican Life may also have their branches there.