I suggest you stay and keep doing your best at what you do. Sarah and/or Tom could (and should) be gone tomoorw. I know how frustrated you are, but you're speculating on what may happen. They may have plans to promote you up to a higher postion. I can tell it's been a rough few months, but it all pays the same, whether Tom is in your dept, or not. If I were you, I'd hang in there for the long haul, and watch what happens. I would also go to your interview, you can never have too many options.