Re-written (hopefully for more clarity)...
There is a difference between disabling and deleting the library in the cloud as opposed to disabling the one on your device.
If you go:
Settings ➔ Apple ID(Top) ➔ iCloud ➔ Storage ➔ iCloud ➔ Manage Storage ➔ iCloud Photo Library ➔ Disable and Deleteon a mobile device or
System Preferences ➔ iCloud ➔ Manage ➔ Photo Library ➔ Disable and Delete on a Mac,
you will disable and delete (after 30 days) the photo library in the cloud.
But if you go
Settings ➔ Photos & Camera ➔ iCloud Photo Library ➔ Offor
Settings ➔ Apple ID(Top) ➔ iCloud ➔ Apps Using iCloud ➔ Photos ➔ iCloud Photos library ➔ Off on a mobile device or
Photos ➔ Preferences ➔ iCloud ➔ iCloud Photo Library ➔ Offor
System Preferences ➔ iCloud ➔ Photos (Options) ➔ iCloud Photo Library (uncheck) on a Mac,
you will disable the syncing of the library on that device with the library in the cloud, but not delete the photos in either place (assuming they aren't optimised on the device). If they are optimised you will need to download the originals (assuming enough room) if you want to keep them on the device.