The only way they couldn't work is if you're having your attributes drained, by a disease or something. Other than that, Restore spells will always work.
There's been a few times where nothing I did worked. I tried casting a spell, using a Cure Disease potion, casting Cure Poison, and my attributes never healed. I had to go to a chapel and pray to restore them. That just happened to me recently in fact, after a battle with some Necromancers.