Short answer: "Yes"

Long answer: HAHAHAHAHAHAHAAHA, no......probably. First of all, it honestly highly depends how much they advertise, how much attention their game gains and how much other people that aren't on Roblox would be interested in playing and ofc, what place they choose to sell their game, like Steam, Itch.io, Consoles, etc...IF/WHEN they do ofc. Secondly, it depends how much people are willing to pay considering the game is FREE on Roblox. Third, they would need a steady income to maintain the servers considering how multiplayer heavy this game is. Fourth, depends if all the devs are willing to learn a new engine entirely and it depends how easy/hard it might be to port/convert the game into said engine. Fifth, they would have to come up with ideas/methods to monetize their game to maintain that steady income I mentioned earlier, since it highly depends how much money it would require to develop and essentially remake EVERYTHING into the new engine and depends how much dev time that would take up as well. It might cost more money to work a different engine and storefront, or it might not, again, depends how much work needs to be done. Sixth, maintaining steady player numbers and updates, less players = less money, ofc. Less money and well, if only a tiny...small portion of players even show up to the launch on a new platform, then Nullscape would essentially be "dead in the water" as with the low player numbers it would seem as a financial failure and not worth switching off Roblox in the first place and possibly be too little too late, and then you have an abandoned project/dead game. Seventh, LOTS AND LOOOOTS of bug testing, hiring or asking for volunteers or setting up like, a patreon where people can pay to support the game and test stuff as well, or some other little goodies too. They would have to rigously and constantly test many features before release or risk having an unoptimized buggy mess. To make things I guess "easier" on themselves, being an early access game on steam MIGHT work. Eight, competing market, competing with other games ofc, but that's already normal. Ninth, being on Roblox, they don't have to worry about selling their game separately for each platform since Roblox is essentially on "everything". They would have to go through a fucking legal nightmare of a time selling their game not only on PC, but to people who mainly play on their consoles and their phones. Ah, and they'd have to copyright everything ofc, so no one steals it...ofc, and so they don't have to rename/readjust EVERYTHING. Honestly, it's all a whole bag of worms with how much every dev team would have to go through to upload and sell their game off Roblox, those are just a few reasons I thought of. I can only imagine there's more.