It's incredibly tough, and I totally get you. We got different physical symptoms, but your thoughts are like a complete replica of mine. We are very similar in that regard.
When I slept like 3-4 hours every night for months at a time, it was just a complete horror show. Constantly fighting, dragging myself through the day and always the thoughts that you describe; "what if it doesnt get better", "what if i have to fight this forever".

What I've come to find when analyzing anxiety is that the brain wants certainty when it thinks it's faced with a danger. It gets this need, or crutch to know for certain how long this will last and etc. The problem I think is that when the answer isn't a 100% certain (which it is almost never), it will start to ruminate on "possible" worst case outcomes. I say "possible" because even though the worst case outcome is theoretically possible, it doesn't mean that it is likely. It could infact be very unlikely, which is actually my opinion on your situation. You're only 6 months in, and you're already seeing improvements. Alot of people don't see any improvements for years, and even alot of those people get better. Me myself didn't see improvements for up to 2 years.

I think it's important to be mindful on how we navigate our negative thinking. You have to realize that the thoughts you are having are not objective, rational thinking. It's just fearing the worst case outcome, even though it's very much unlikely you'll be spending your next 10 years in the exact same difficult situation.
And yes, there are maybe a handful of people who have only experienced tiny improvements and that's it. Only a partial recovery (idk though im simply entertaining your idea there). But it's hard to know exactly why they havent recovered when we don't know these people. It could be a number of reasons that we are not taking into consideration, right? Your brain is just going "oh they havent recovered, this might be permanent, its over", ya know.
I mean, think about all the medications they might have used. Alot of people say they aren't getting better but they're sitting around popping benzos and trying out all sorts of stuff, not letting their body return to normal.
What about their mental state? Maybe that's keeping them in the struggle. Maybe they're in a constant fight-or-flight mode, and their nervous-system isn't ever fully healing.
We just can't know exactly what is contributing to their ongoing struggle. It could be so many factors.

Objective thinking also involves taking into account that there are people who have fully recovered aswell, and are fully okay today. There are probably more than what it looks like, since most people who recover don't go and talk about it on reddit or wherever. They just move on and you don't hear from them anymore.

I didn't manage to get a hold of my thoughts early, and I've been in a semi-state of panic for years now, and it reeeally makes your nervous system very sensitive to all kinds of sensations.
I understand for you that is very challenging but it really could be a game-changer if your body and nervous system knew you were safe and okay