The below is copied and pasted from our DOT website. It indicates that if your airline cancels its flight you are entitled to a refund rather than a voucher. I would much prefer a refund because who knows for sure what the situation will be in the future. Unsurprisingly, airlines may be playing games about this. An article in USA Today shows that United is definitely doing so. My taxes are already contributing to the airline bailout, so I am not eager to contribute further.
”If your flight is cancelled and you choose to cancel your trip as a result, you are entitled to a refund for the unused transportation – even for non-refundable tickets. You are also entitled to a refund for any bag fee that you paid, and any extras you may have purchased, such as a seat assignment.”