This traveler had already paid for the airline portion of their trip. Later, they noticed a price drop and negotiated for a better ticket price. The airline gave this traveler a credit to be used toward future travel, not a discount on the current trip.
This traveler had already purchased their travel insurance as well, was within their free look period and wanted to know if they should reduce their trip cost to account for the future credit.
Why was this savvy traveler concerned? Because they had purchased travel insurance with a pre-existing condition waiver and cancel for any reason coverage – both of which require the traveler to purchase coverage for the entire non refundable charges of their trip. If their trip cost was now reduced, this traveler wanted to be sure their coverage was correct.
In this case, however, because the airline credit was toward future travel and not the currently insured trip, the traveler should not reduce their trip cost.
Had the airline issued an immediate credit on the current trip, then the traveler could lower their insured trip cost to avoid paying for more coverage than they needed.