Thank youThis is still the same. If you enable iCloud Photo Library, PhotoStream disappears. And it reappears when you disable it.
You're able to use PhotoStream without backing up your photo library. That's what I do. I save my photos somewhere else. My pictures would take a huge amount of my iCloud storage space, that's why I don't use the backup for them.
Also, your pictures will behave as normal. Again: I don't export mine to iCloud. As long as I don't delete them from my Photos app, they are there in Camera Roll (or Recently Deleted).