Ooh, I’ve actually thought about this one a lot
Viktor stays a very good friend of the Weasley/Granger family, so much that Hugo and rose call him “uncle viktor” (even though he’s not related). He is probably kind of rich because of his fame as a quidditch star, so every christmas he comes over with a big bag of presents, like a Bulgarian Santa Claus.
Bonus: Fleur and Viktor stay very good friends and one night at a bar, a drunk Fleur and a less drunk Viktor make a bet. A one-on-one quidditch match. Loser has to name their firstborn child after the other person. Viktor wins, obviously, and that is why bill and Fleurs oldest child is named Victoire.