I feel like Cassian will still be king in the end if he atone for his sins, and ofc with the condition that he will not kill his brother. Then it’ll be a win-win situation for them
She transmigrated into the villainess' body(not sure if it was a novel She read in her previous life cause I don't recall much )and then her engagement with the prince was annulled the reason being attempted murder and more on the ogfl (the saintess) she leaves the capital to live in the northern territory and summons a demon. I hope this helps
Finally, she told them abt the disease. That's a relief