My wife tested positive before our Northern Lights cruise in January and we got a complete refund (minus the cost of insurance) about 30 days after filing the claim with TripMate.
After reading the cruise contract, I tried to get Viking to refund the fare under the terms of the contract, but they pushed me to file an insurance claim first, only promising me that they would reimburse me for any shortfall of the insurance claim, which there wasn't.