They are trapped until someone manages to save them! It's not impossible for them to find a way to escape or to have someone bust them out - so how long Alberto is kidnapped is up to you. It could be a couple weeks, or even just a couple hours when someone notices and goes "hey no".

Basically, it's still possible for him to go to Tir Na Nog. Since the fae are still rebuilding their court, it's pretty feasible to escape if you have help.