Have you been using My Photo Stream previously and recently? If you have not used this particular cloud service, there is nothing to worry about. iCloud Photos and Shared albums will continue to work as before.
If you have not been using My Photo Stream to transfer photos between your devices, there is nothing to worry about.
My Photo Stream is just a very convenient cache in iCloud, that is holding copies of the most recent photos from each synced device - at most a thousand photos at a time, and only for thirty days. The photos themselfves will not be removed from your devices, just uploaded to the cache in icloud for syncing, where the other devices can grab them. A mac will download the photos from this cache automatically and add them to our photo library, on the mobile devices we have to download them manually. If you did not have My Photo Stream enabled on any of your devices during the last thirty days, there will be nothing to save from it.