I’d guess it’s defaulted to credit, but shouldn’t matter. You should be able to request an ETC instead, or a refund since flight itself will cancel - agents don’t seem to be pushing back on that option any longer (even if all aren’t offering the option - you may have to ask), though refunds are slow. Just talked to an agent to find out the status of mine (requested online on March 23, though res. doesn’t seem to be able to see it was made, but could see my second request done over the phone on Apr. 4, by phone). Seems most refunds are taking a long time - agent just told me 3 weeks, though some have reported seeing it back on their cards in 3 or 4 days. Requesting a refund online is another option.

to find out if your flight landed up as credit (most likely), log into United.com, click view/manage reservations under my trips menu, then click the canceled tab. Your itinerary should be under there, with a button to ‘use future flight credit’.