This wasn’t sudden. Fox knew he’s not returning.
That's why they have no one lined up to take his place.
Seems they would have had a joint statement instead of being blindsided, but everyone can believe what they want.
Yup they were prepared.
"We are extremely proud of our journalism and the stellar team that Chris Wallace was a part of for 18 years. The legacy of Fox News Sunday will continue with our star journalists, many of whom will rotate in the position until a permanent host is named."