If you cancel for a covered reason, your insurance should pay any amount you don't get reimbursed for. For example, Regent cancels cruise and reimburses you full amount--then no insurance claim (minus insurance cost, as you note).

Here's Regent's current policy:
https://www.rssc.com/coronavirus-statement

Most cruise lines, when they cancel, have provided full refund, but--to entice you not to take the refund, have offered a 125% future credit option. It's usually the passenger's choice.