User blog comment:Dracoliche/Things to come.../@comment-24053170-20190801174946/@comment-24053170-20190801180727

The real only notable differences between the ending of the 4th seasons wedding and the LN's ending is the fact that Louise and Saito have their wedding night together and Siesta is allowed to be Saito's mistress.

Really other then that, the wedding is exactly the same as the anime,

Saito does return home, but its implied to be a one way trip due to Void Magic no longer existing.