It's been over 120 days since you opened Cloud Shell from the Google Cloud Platform console. In 7 days, your Cloud Shell home directory will be automatically scheduled for deletion. Hello Steve,
Cloud Shell is a free-to-use tool provided in the User Interface that one of it’s features gives you access to a hidden instance in the background with pre-installed packages, and is always ready to use. The idea is to help Google Cloud Platform users to get started quickly, not to worry about basic OS packages/tools, and also, avoid the need to create a dedicated (usually paid) instance for development, troubleshooting … etc.
The notification is simply informing you that it has been a while since you have used the tool, and while using it, if you saved any files on that “hidden” instance, they will be deleted. I believe the deletion should not affect your RADIUS instance, as it is not related to the cloud shell instance. However, if you have anything important saved on that cloud shell instance (Home directory), and according to this note, you can just click the cloudshell button in the UI, and that should reset the timer, but you also should consider moving such files to a different medium like Google Cloud Storage. For more information about Cloud Shell you can check this document.