Well considering how they made huge alterations to the plot of the first movie, I really wouldn't be surprised. I don't know whether they have the plot planned for the seconde one, but if they didn't even mention what happened to Thalia of her boom of anything, then they might not be planning on putting it in. However, I wouldn't be surprised if they pulled that movie BS and just added the story in, but only when they needed it. No foreshadowing allowed in movie theatres apparently. I too would be very upset if Thalia wasn't in it.