For me personally I believe that the Slann are all floating around in their temples in Azyr and only going down into the Mortal Realms surface to do battle. The main weakness of the Seraphon is that I get the feeling that while all other Seraphon can be respawned in the pools the Slann cannot. If a Slann were to die then their constellation will surely perish and considering how few Slann there are then this is a very tenuous position to be in.
To be fair though, with the exception of the very early Fantasy fluff which had Slaan emerging from spawning pools, that's always been the case for the faction. The Slaan are finite in number and can't be replaced. It's just like the Elves really. I believe it was Phil Kelly who was asked once a question along the lines of "The Elves are supposed to be a dying race yet we see battles where thousands die. Shouldn't that be a huge blow to them?" To which Kelly replied "There's always enough Elves for any story we write." Meaning that thematically, the race is doomed, but they never actually reach that point. With that in mind I suspect that the Slaan will be in the same boat (or starship as it were). Some may die, and from a story perspective, this would mean eventually the Seraphon would be finished. But we'll never actually run out.
Try picturing an object so big that it underlies an entire city and the outlying land. Scaling up to that would work for me... But in... A thread from several weeks/months ago. ...I was fine with a ship shaped like an inverted pyramid that was 2-3 miles across, measured at its base. Nice that GeeDub is onboard with the concept.
Yup, there’s a couple novellas of material at least on board that ship...come on GW....get it on the things to do list. Tantalising. As an aside, I played a small open war cards game with my mate the week that story got released and heroes I chose were a skink star priest and a sunblood so that was a cool coincidence when I read it. I never would have set it on board the ship though.