Fuck it, I'll talk legal bullshit anyway:

The UHC application has no danger of disappearing at all --- it is licensed under the 'copyleft' GPLv3, which stipulates that even the original authors cannot stop others from using it, distributing it, or building onto it. These terms also mean that HICU (or anyone else) cannot suddenly lock the application from the public, as these requirements of free distribution and building-onto-it (the source code must also be given when asked) are true for whoever falls under the terms of the GPL. If someone does not abide by these rules of 'forced'-openness, organizations like the Software Freedom Conservancy are willing to litigate such cases to make it public again.

The UHC asset pack is a different story. Of course it contains original artistic material by Hussie, Homestuck Inc, and contributors. But have all those contributors --- even the super early days ones --- signed a written contract that says the material can be distributed in other forms than just being posted on the official Homestuck website? What about clear 'influences' from 90s media strewn throughout Homestuck, from Con Air and Armageddon all the way to Mac And Me and Little Monsters? These could be seen as parody (exact boundaries of this differs between countries!) or 'fair use' (which is specific to the US and only granted on a case-by-case basis, there is no 'blanket fair use' thing in US law, and thus would need a court decision to be clear), or transformative (use in existing Google Image results for e.g. the Prospit and Derse landscape collages), but others are more worrying (Homestuck has both structural and visual 'inspiration' from The Neverending Story). And even Gio talks about the asset pack containing Adobe Flash binaries (property of Adobe, known to be 'annoying' about copyright). Hence, what happens to this is a bigger question. The HICU currently hosts it, but this is probably also only contingent on flying under larger companies' radar.

But there is a larger issue than just copyright (which I guess steals all the thunder, considering e.g. the semirecent Dolphin-vs-Steam kerfuffle, or anything involving Nintendo really), and that is software maintenance.

Operating systems change over time, and applications have to take these changes into account, otherwise their functioning will degrade over time, and will even stop working at one point. And this is besides fixing the currently-existing issues in the UHC application ( https://github.com/GiovanH/unofficial-homestuck-collection/issues , wew, 195 of them at the time of writing!). Currently, it is very unclear who will take up this task (the HICU, maybe????). It's possible that competing 'editions' will emerge. This is also what happened to e.g. Citra after the Yuzu organization got shut down: some people are trying to keep it in working condition, maybe fix a few issues, but they are much less familiar with the codebase, they don't have as much time, and so on. Youtube-dl had a good ending to this, as yt-dlp is currently the 'gold' standard. Let's hope this will also be the case for the UHC.