Well, I started this off just wanting to mention a few salient facts about the Troll's game, but it turned into a dissertation on the mechanics of Sbrub, and the fates of those who play it. May be interesting, maybe not, but I enjoyed writing it.
Think for a moment about what Sburb is; it's a computer game, albeit a game that's physically interacted with because it physically exists, but it's still born from a definite plan and works by definite rules. When the game starts, it forms it's own separate pocket universe, labeled "The Medium" by itself and a session by Karkat, which is correct. Within that Medium-session are Skaia with the Battlefield at its center, the planets Prospit and Derse and their chained moons, the Veil full of labs and factories where the light and dark armies are made, and however many themed planets are created for the game's players to act in. The Medium is populated by a stock cast of characters and all those standard elements, plus the planets whose content is generated with each session. Different bandicoots and all that. The actors are scripted to perform by certain motivations; differences are caused by the players and their guardians interfering with Sburb's stock plotline. It's important to remember that this all exists in a universe removed from the planet that the players actually come from, and has its own laws of reality. The Medium and (what we'll call) the homeworld are distinct places, that can interact with each other by way of Skaia's portals.
Where Sburb comes from is a complete mystery so far, but once activated, it functions a lot like how Lord English is described. The Medium doesn't exist until a player joins the game and enters it. But once created, it populates its own history backwards through time, and winds up effecting the homeworld's past in the process. Technically it never existed before the game starts, and technically it always existed; players entering and generating elements are just a temporal formality.
Sburb is also responsible for creating the players themselves, their guardians, the First Guardian, and the exiles, and probably lots of other junk too like the Frog Temples. It accomplishes this by generating all that stuff in the Veil (how, when, and why is still unclear for elements besides the people), then the Black Royalty hurl the Veil into Skaia, in the Reckoning. Skaia tries to defend itself by sending most of the asteroids through portals to the only place it can open them, the players' homeworld. Some are sent into the extremely distant past, planting the Temples and the First Guardian. Some are sent to the relatively recent past, seeding the players and their guardians created by those in the session. Some are sent into the future, seeding the exiles and the labs they will use to advise the players (see: Egg, Apple, and Bottle). But most are sent concurrent to when the game is first started in the real-universe, usually demolishing the houses of the many players not part of the paradox-loop already seeded. (Other important thing to remember, win or lose, the planet the players come from is slated to be toast by the end.)
These already offer a few different takes on the concept of fate. On the one hand, the actions of the stock characters are hard to call Fate, as that implies alternate paths that could have happened. They're as fated as any program is to follow it's prewritten instructions. But the players are a special case. Does Sburb choose the small circle of people who will survive to play it? Or does whichever closed loop of players who happen to survive long enough to create and place their paradox clones retroactively guarantee that they will be the ones to play it? The name of the game in Sburb is paradox loops - things that weren't guaranteed until they happened, but whose actions involve seeding their own impetus so they have to happen anyway. Even the aftermath of the game seems to be set in programming - the big labs and interactions of the exiles seem way to obvious and detailed to be anything but intended by the game's instructions.
Where I was trying to get from the beginning though is the eventual state of the players' homeworld. It's clear that Sburb can effect the homeworld with gates, but it's not clear whether the players can ever choose to do this. Pretty much everything says they can't, that once each player enters the Medium, they can kiss their world goodbye. There are possibilities; hitching a ride on a Reckoning meteor could work, as it does for the exiles, but their particular client-server sessions having already started, it's hard to say how they could get back into the Medium if desired. There's also whatever Grandpa Harley did, who just sailed to Earth, as did the White Queen in the kids' session.
And now I'll get to the point. Karkat believes his universe is coming to an end, from the glowing graph of doom, probably very soon. We already know that Alternia itself is still around centuries in the future, and Snowman narratively comments that she possesses all the time in the world, whatever that means. Remember my posit, that the Medium is a universe completely separate from the real-space of wherever the players' come from. Perhaps that is Lord English's purpose, not destroying the universe, but entering and destroying the game universes. There's the further complication of the Distant Servers where Lord English's program (and probably the Walkthrough and presumably the Horrorterrors) reside. Theses are all good hints that the Trolls may be able to escape from their Medium, either to another universe or back to the wasted husk of Alternia.
Whaddaya know, I'm a professor of Skaia paradox physics now. Maybe I'll finish my research dissertation on what happens when a player goes through their second gate to a planet whose owning player hasn't entered the game yet (as Dave does at the end of Descend), or whether players in the Medium need to eat (alien biology aside, the Trolls were there for most of a month), and earn my Doctorate of Skaian Physics.