From things said by the likes of Ty Frank and Naren Shankar since the end of the deal with Amazon, it's been pretty clear they were already in the process of continuing the franchise elsewhere in some form or another. Apple makes sense as the next home for the franchise as it's the only major streaming service that's still both willing and able to throw money around for the sake of prestige projects, while the others are making big cut-backs. That doesn't prove anything of course, but it at least seems logical.
Honestly I'd be surprised if they go straight into the final three novels given the three decade time-jump in the books (though I suppose they could credibly cut that in half for the sake of the adaptation), and would expect to see more of a spin-off project or indeed; projects plural. After all 'The Expanse' originated as an RPG, and that's what all the world building was developed for. As a result it's ongoing narrative need not always be inexorably tied to the adventures of the Roci crew. There's enough of a living world that they can tell almost any kind of story they want, up and down the timeline.
A Belter/Transport Union show would seem like the natural choice, maybe acting as a bridge for when the eventually do catch up to the events of 'Persepolis Rising'. Or they could wind the clock back the the early days of the expansion out into the Sol System and do something with the Martian secession and the early belt settlers. They can't really go the opposite direction given the ending of 'Leviathan Falls', but they could set something contemporaneous with the original show with a new cast and either a new perspective on events, or just have those events as a backdrop, incidental to the lower stakes plot for said new characters.
