We have two types of license, evaluation and permanent. We could use evaluation license three times, normal evaluation key is valid for 30 days, so overall we could use for 90 days.
After 90 days, if it AP license then APs will disconnect from controller and if it is pef license controller will reboot and it block features which it is related too and will loss the configuration.
make sure you have configuraiton backup, if you fail to renew your license.
Regards,
Pavan