You don't need to delete a Mac to free up licenses, just set them to "Unmanaged" by un-checking the "Allow Jamf Pro to perform management tasks" checkbox. Make a view for unmanaged devices that are checking in so that you can make them managed again and take action.
iPads are a little different in that there is no Jamf binary, so your only option is to click the "Remove MDM Profile" button but this will also (obviously) result in a loss of control over the device.
With how critical MDM is, deleting a device record will immediately result in you losing control or visibility on the device, which is probably not something you want to do.
Remote locking with a message to contact the Helpdesk is a good way to get a user's attention and bring them into compliance, but if you have an EDR such as CrowdStrike you can contain the device so it can talk to nothing except the EDR.
You could also look at swiftDialog and make the prompts full screen so that users are less likely to ignore them.
