I'm DM'ing this adventure currently (though I've changed Cahokiantep to incorporate another city in the players' Campaign) - and the players are loving it (I think !). The players have just completed Scene 5 - and we're about to start Scene 6 which will lead, of course, into Scene 7. Have you created the second installment ? If not, I'll just have Xavier Melton show up before it gets too far into the astral rift situation and tell the players to get out of the city as quickly as possible ! At which point, the city will disappear into the Astral rift. But if you're well into the second installment OR if you have some recommendations of adventures on the Astral Plane, I could suck the adventuring party into the rift...!
Apologies for answering this with a wholly new post, but I don't have anything else scheduled for today, and any chance to talk about my work is a good one.
The next installment is going to be called Cahokiantep: Journey Across the Universe, and no, I've not started writing it yet. I have a general concept and a basic outline--two, actually--but I haven't allowed myself to sit down yet and start nugging out the details. That said, C:JAU is going to be a kind of sea story set in space. Think 20,000 Leagues Under the Sea-meets-Starblazers. I even started reading 20,000 Leagues while I was on vacation with the specific purpose of understanding its story-beats, so that I can incorporate at least some of them into this adventure.
-- C:JAU starts six months to a year after Cahokiantep gets shunted into the Astral Realm.
-- The city has adapted, and life is returning to normal, but where there once was water, now there is the infinite mass of the Astral Realm. Since Cahokiantep has a river running right through its center, this is a big deal.
-- Then Xavier Melton gets contacted by Starsha of Iskandar (granted, I will have to reskin some of this), who offers them the Wave Motion Machine as a way to get the city home. At this point, you may remember that the Cosmo Reconduction Device caused the problem in the first place, which I point out only to note that the Starblazers allusions were built into the narrative purposefully at the very beginning.
-- The PCs set out in their captured turtle ship for the far side of the universe, have a shipwreck, and wackiness ensues.
-- I still have to figure out how obsession and revenge figure into this narrative, and I don't have the first clue about the specifics of the encounter structure.
At this point, I think you have three options:
1. If I was running your campaign and committed to waiting for C:JAU to be released before delving into the Astral Realm, I would have the city disappear, leaving the party behind inside a giant crater. I would offer absolutely no explanation for this because that sets up a long-standing mystery, i.e. why were we left behind? When you have Xavier Melton pull the party into the Astral Realm later, you can explain this away and set up the new adventure.
2. Allow the party to cool the CRD down, so that the city is not pulled into the other Realm. You can have it malfunction later at your convenience.
3. Find a seaborne adventure on Merric's Musings and run that, adapting it as necessary to the Astral Realm. In your place, this is what I would do personally. I would substitute any risk of drowning with a risk of contracting Astral Madness or a reskinned form of Cackle Fever.
Does that help?
I'm currently writing a novelisation of "The Mystery of Mordecai's Monster" for the Sneax & Elaina Emboo series, and after that, I'm going to do a short story for the same (3rd) installment about one of the villains from the Crown of Pluto. When both of those are drafted, I'm going to (finally) put together C:JAU.