The last we see of Kreacher in the books is at the Battle of Hogwarts.
The house-elves of Hogwarts swarmed into the entrance hall, screaming and waving carving knives and cleavers, and at their head, the locket of Regulus Black bouncing on his chest, was Kreacher, his bullfrog voice audible even above the din: "Fight! Fight! Fight for my Master, defender of house-elves! Fight the Dark Lord, in the name of brave Regulus! Fight!"
(Deathly Hallows, Chapter 36, The Flaw in the Plan).
I'm aware of this humorous tweet from J. K. Rowling about Kreacher's fate but I'm not sure it can really be taken seriously. I'm interested in if we can confirm whether or not Rowling has said anything else on what happened to Kreacher after the Battle of Hogwarts. Specifically, did Kreacher continue to serve Harry and the Potter family in later life? I'm conflicted on whether or not Harry would be OK with having a house elf as a servant. On the one hand, he wasn't as convinced as Hermione about opposing the practice of keeping house-elves. On the other, he did free Dobby from the Malfoys.
So has Rowling said anything else on this subject? If not, can we deduce with canon-based speculation whether, on the balance of probabilities, Harry would've kept Kreacher or not?