On which devices have you been using My Photo Stream? Is it still enabled on one of your devices?
The "My Photo Stream" album will not be shown in Photos, if it is disabled on the device, or if you are using iCloud Photos as well. Then the photos from My Photo Stream are included in "All Photos", but not marked as My Photo Stream photos.
The way "My Photo Stream" has been working, is to upload any new photos you import to Photos to the My Photo Stream album and keep it there for at most thirty days. So each photo in My Photo Stream will be somewhere in Photos on the device, where it has been uploaded from, unless you already deleted it from this device.
- If My Photo Stream is enabled on your iPhone, you should be seeing it in the "Albums" section".
- If My Photo Stream is enabled on your Mac, you should be seeing it in the Library section".
If you are not seeing an My Photo Stream album on any of your devices, there is nothing to save. Are you using iCloud Photos as well? Then the My Photo Stream photos will be mixed in between your othe rphotos in All Photos.