Depending on which message you are getting there may be a grace period of a few days after the expiration date that SAS will continue to run. The log will be full of warnings that you are in the grace period if there is one.
After the grace period expires you basically will not be able to run any SAS work, data step, procedures, anything. Every attempt wll get a "license expired" of some flavor.
Best, contact SAS and get the license renewed.