Would signing out of iCloud delete my locally stored photos?
iCloud always asks you if it deletes local copies and it only deletes copies it knows are stored online, so you should be safe to remove an account.

If you're worried, make an iCloud and iTunes back up just in case, but signing out only is intended to clear things that came down from the cloud and even then it offers you the option of keeping local copies of data in many classes of data (contacts is the one I see often).