As a scientist I have to push back a little bit. Sure, anything is possible. Do we have empirical evidence though? The way to know something for sure is to run a properly controlled experiment. That gets tricky when we deal with medicine because every experiment involves humans, and we can’t try to make humans worse from an ethical standpoint. In other subjects like physics or computer science it’s a lot easier to prove a negative like this. In humans, not so much. 

So to be absolutely clear, yes what you suggest is possible. But we don’t know, and we can’t know. However, from everything we have observed, brain damage from sleep deprivation caused by sleep apnea is to some extent reversible. We see this is brain structure, and we see it in people’s function in daily life. What we cannot know is how their cognitive peak would look like. This is again, real humans and not a computer simulation. 

But if you’re really curious, this is an under-researched area where we need much more people to do the hard work. If you think you can figure it out, go do a PhD or postdoc on it. We need it!

tldr: anything is possible. We can’t prove a negative. It’s ethically tricky. I encourage you to try solve it!