"If you turn off iCloud Keychain
When you turn off iCloud Keychain, password, passkey, and credit card information is stored locally on your device. If you sign out of iCloud on that device while Keychain is turned on, you're asked to keep or delete that information.
If you choose to keep the information, it isn't deleted or updated when you make changes on other devices.
If you don't keep the information on at least one device, your Keychain data is also deleted from the iCloud servers."
https://support.apple.com/en-us/HT204085