Miliza Morelle died between House of Dracula and this movie.
That's why we never see her.In relation with Miliza's probable death...
Dracula killed her. That's why Larry Talbot is not more the same depressed man as the past movies. He wants vengeance against Dracula, and becomes a vampire hunter. He is more serious than depressed. He is really angry.The main monster trio survived.
They survived worse things. They really never die.- Confirmed in Return of the Wolf Man. Of course, if it's really canon currently.
