"The teacher must die" is a classic trope and one that works well for many types of stories, but even great stories don't always execute this part in satisfying ways. There are small details and nuance in the way that Serie is prepared to die. The flags and setups are done in ways that try to convince us why she will or should die. If true, her death would be more satisfying (or less unsatisfying) than just following a trope. For example, Serie gives out reasons why she picked these mages to guard her, what she wishes to see for the future, etc. These are also subtle reasons why she should die (subtle for the characters, less so for us). This is great because she's literally giving us reasons to accept her death, and it's a part of the future she wishes for. In turn, we are more likely to accept her death (provided the rest of this plotline is also executed well).
On a side note, the author is so goated that I wouldn't be surprised if he used all the flags as a red herring or bait & switch on us, and that he has something else planned for the story. Plus, Sense could always die later or the problem of the teacher role gets resolved some other way.