Cancellation of my stream photos

My Photo Stream is a separate service to iCloud Photo Library as explained in the support document you posted from.

Do you use "My Photo Stream"? Do you see a "My Photo Stream" album in the album section of the Photos on your iPad, iPhone or Laptop?

Do you have My Photo Stream enabled in Settings -> Photos -> My Photo Stream on your iPhone or iPad?

If the answer is no, to all the questions above, then you do not use My Photo stream, and you will not lose anything.

If the answer is yes, then you would only lose access to said photos from the devices that did not take them. Photos on My Photo stream are also on the device that took them and will remain on that device when My Photo Stream is shut down.

If you use iCloud Photo Library, then all your photos are already accessible to all your devices that have the iCloud Photo Library turned on in Settings -> Photos.

If you are using iCloud Photos on all your devices, then you have nothing to worry about. To verify on iPhone/iPad, go to Settings > [name on top] > iCloud > Photos and make sure Sync this iPhone/iPad is turned on. For the Mac, go to  > System Settings > [name on top] > iCloud > Photos > Sync this Mac.

You're welcome. Glad I could help.