That wouldn't fix it since the base problem of Book 3 is going against the previous characterization and twisting whatever the character is like according to the needs. The damage has been made already.
The only thing that could make it somewhat right is if every character reminiscent of Book 3 finds Simon as the victim and hates Grace for it. Samantha, Hazel all having resentment and hatred over Grace and having some sympathy (not much for Hazel given her experience) for Simon. Plus stuff like Amelia realizing she was 100% responsible for them and took no decision to help them out, leading to the death of a man, and feeling awful about it.
If Book 3 is supposed to be a tragedy then treat the only actual tragic thing as it should be, not the demise of a "monster" of your own creation. Because Hazel is off with a better mother figure, Grace is still alive and able to fix things, the apex are all starting to grow and stop being shitty, and Tubas murderer is dead. That is not a fucking tragedy, Simon is the only tragic character here.