I don't think the prediction that he'll literally come back is in any contention. Many other characters will be making an appearance in the final saga in some capacity after all. Probably even BM and Kaido who are "dead".
The question is, will he be relevant, much less pivotal, to the plot in the same way he was in Wano? I think that's a toss-up.
Yes, he has had build-up that requires a satisfying arc and conclusion to his story to justify his presence in the first place.
However, if you observe the general patterns in the story, you'd long have realized Oda has been over-crowding it with too much shit in general. And much of it doesn't lead anywhere or conclude in a satisfying manner. How many times has he over-indulged on things he finds interesting in the moment, then quietly ignores indefinitely? The Straw Hats are the pillars of this story, and Oda has demonstrated that even they are not immune to this irresponsible behaviour.
If Kid makes a token appearance with no narrative substance (or no appearance at all), can we really say he'd be an anomaly? Or just another one of Oda's tossed-aside playthings that he couldn't conclude in a satisfying manner?