People are having online chats with google and are being told they will not keep Photos once they cancel. So I think it's safe to assume that if there's not an official google page saying "you will not lose your photos" etc you must prepare for them to vanish either immediately or at any point in the future.
The official FAQ has been updated with the following:
"What happens to my additional Google services and paid content if I don’t want to pay for Google Workspace premium features?
If you don’t upgrade to a Google Workspace subscription, you will not lose access to other Google Services, including YouTube, Google Photos, and Google Play, nor paid content, including YouTube and Play Store purchases."
