deleting photos

It depends on what you mean by "original photos that are on the hard drive".

Lightroom will keep a temporary copy of some of your cloud-based originals on the local hard drive (it will keep a copy of all of them if you've checked the "Store a copy of all originals...." option in the Lightroom Preferences), and if you delete any originals in the cloud any locally stored copies are eventually deleted. I say "eventually" because when you delete any images from the cloud they are stored in a "Deleted" collection (basically a cloud-based "recycle bin/trash can"), and they remain there for up to 60 days to give the user the chance to undo an inadvertent deletion. So that deletion of the local copy only happens when the original in the cloud gets permanently deleted from the "Deleted" collection, either when the 60 days are up, or if the user decides to use the "permanently delete" option before the 60 day period expires.

However, if you had image files already on your hard drive which you then added to Lightroom, those original images are outside Lightroom's control and so would never be touched if you delete the cloud version.