If you turn on Advanced Data Protection you will still have access to your photos as long as you have the correct "keys" but if you lose your keys no-one not even apple can help you gain access to your photos again, as they are encrypted with the keys
There are several steps you can do to make sure you never lose the keys. Your trusted devices stores a key,
you can write a key down, and you can dessignate a recovery contact that can help you regain a key if you have lost it.
This explains more about standard and advanced data protection:
iCloud data security overview - Apple Support
And whatever you chose to do, it is never a bad idea to make sure you have saved your photos in more than one place, like for example keep an offline backup on a external drive. Don't put all your eggs in one basket.