Maybe this question can't be answered yet, but what happens if Aliza dies? Does she "come back" like Frisk was capable of doing?

If Aliza dies, she is gone for good. She can’t use the save stars (any that remain, that is), for several reasons yet to be explained… but no, there will be no coming back for her if she perishes. The consequences of harm and death are real and lasting for her. It’s one of many reasons Sans is so protective.