It was always below the 'go to the guard barracks' option :/ no idea why it's gone, I even went to Rais' house and my character said that she had to go and save him
Are you still stuck? If you are, you need to go to the market during the evening (and evening only I believe) this allows you to sneak back into the castle. The option to go to the castle under the 'barracks'' was removed after it was revealed that you were a demon (I believe) and your objective was to destroy something, so charging though the front gate is probably a bad idea. Hope this helped.