A large part of the suspense in a horror/monster movie is not knowing who will survive and who will die (gruesomely) at the hands of the monster.
When you know the outcome, the suspense is gone and all that's left are some jump scares.
Demeter has not really drawn me in just yet (read: I have not seen it), but I do hope they did something with maybe one or two characters surviving in the end, but not being on the ship when it runs aground, or it will lose any suspense for me...