Honestly, I think you're worrying about the wrong thing. LibreWolf isn't really a "full" browser, it's mostly a set of patches and privacy settings on top of Firefox, while Mozilla does all the heavy lifting on the engine. That's why it updates so fast, and why a small team of volunteers can keep up at all. So the real long-term risk isn't LibreWolf slowing down, it's Mozilla itself. If Firefox ever dies, LW dies with it, there's just no way a handful of people could maintain a browser engine on their own.

That said, the project has been around since 2020 and has never fallen behind so far, so I wouldn't loose sleep over it. And even in the worst case, your profile and extensions are 100% Firefox-compatible, so switching back (or just hardening stock Firefox with a user.js like arkenfox) would be trivial. Worst case scenario, you lose nothing but a bit of convenience.

Also worth saying: if you like LW and want it to stick around, you can help the project in whatever way fits you thé best. Doesn't have to be code, talking about it around you, reporting bugs, or any kind of support goes a long way for a small FOSS team like this one.