In the previous chapter, we mentioned that the father of Olivia and Cirilla, Emhyr, wanted nothing but the crown of Nilfgaardian. He had long planned his ascension with Vilgefortz's help.
To leave as a family member of the "Lioness of Cintra," Queen Calanthe was not an easy task. Being a family member was another matter of hardship.
Therefore, Vilgefortz and Emhyr had engineered a plot to fake their deaths in a shipwreck. Pavetta, Cirilla, and Emhyr would be "dead," in the deep sea with Vilgefortz guaranteeing their safety.
Olivia was never meant to be part of the "survivors." Although Vilgefortz was a peerless strategist, adding Olivia to his band would greatly increase the risks of failing. He did not have any use of Olivia now, other than being the newfound love of his secretary. For the sake of his subordinate's loyalty, Olivia must be alive.