I assume that the insurance company won't sell a policy that is unfavorable to them in expectation. The way insurance companies make money is to set their rates so that they win on average. If you buy both life insurance and longevity insurance, you'll find that the payments you put in exceed the value of the payout, at least in expectation.

Put another way: you're dutch-booking yourself, not them.

Or have I missed a nuance here?