Deleting photos that have been backed up iCloud
Yes, it could be gone over a period of time as more backups are made and you're forced to delete older backups (or if you remove Camera Roll from the backup selection). The next time the iCloud backup happens, it will create a backup without this photo. The older iCloud backup with the photo will continue to remain for as long as you have space available on iCloud and you don't delete old backups.

To view the available iCloud backups for your device, go to Settings > iCloud > Storage &amp; Backup > Manage Storage.

Note that iCloud backup happens  automatically over Wi-Fi every day (only once every 24 hours) while it’s turned on, locked, and connected to a power source. You can also trigger it manually from Settings > iCloud > Storage &amp; Backup > Back Up Now.