If you feel that you'll be taking on the responsibilities of someone who was previously your boss (and I'm therefore assuming a higher paid position in the comp

If you feel that you'll be taking on the responsibilities of someone who was previously your boss (and I'm therefore assuming a higher paid position in the company), then I'd argue that you have every right to -- at the very least -- ask about the options. If they value your contributions so far enough to give you more responsibilities, then they should be open to increasing your compensation, too. Good luck!