I don't think it will be Thomas. That seems too "easy". And since we've got books and books to wait, we can't be sure Thomas will even be alive; we know how much Jim likes torturing Harry!
But Jim's second favorite pastime is torturing Thomas if you think about it so i would be more worried about Justine making it to the end.
Thanks to Linklele for my new avatar!
If i had superpowers. I would go to conventions dressed as myself, and see if i got complimented on my authenticity.