I grabbed this from the following FAQ:
https://www.cisco.com/c/dam/en/us/products/collateral/software/one-wireless-subscription/q-and-a-c67-739601.pdf
Question: Several customers believe that when their subscription expires, a Catalyst 9K will not work. Can you confirm if L2/ L3 services will work if the license has expired? Y
Answer: Yes, the switch will continue to function, however the customers will not be entitled to receive updates/upgrades for the functionality in the DNA stack. Customers must renew their subscription to continue to get access to the DNA innovation. L2/L3 services will continue working, and customers are entitled to receive updates/ upgrades for this functionality, as they are tied with the perpetual network OS: Network Advantage or Network Essentials.