Memes aside, Hamilton didn't go to Ferrari because he believes he will win. He saw what Mercedes was doing and he realized that he can't get a win there, no titles, so he might as well go race for a few years as the most known brand all around, Ferrari is THE racing team, in all over the world at all kinds of races.
And now, he is just having fun, doesn't even care that much, care enough that he wants to give his all, but he is not expecting a title. He knows his title times are gone, so he just focuses on being happier and just be a Ferrari guy. So there is no way he would go back to Mercedes, there isn't anything that makes sense for him to go there. With that being the case, I am sure that we are going to see him stay there, and Max will be at Mercedes instead.
Maybe... But then again and as I said before, Hamilton has a knack for going where new rule changes could make a team do better. People prolly are memeing that ain't doing really well at Ferrari. But let's see what happens next year after the rule changes.
And I do hope Ferrari gets Horner. But it's not looking likely with Alpine giving what Horner wants. His chance to be like Ross Brawn where he could be the owner and team principal.