Satoshi will most likely use his coins.
Why wouldn't he?
Being the creator makes him an early adopteder at the same time.
In fact, he's the first adopter and he devoted so much time in something that he didn't know how will end.
Now he owns hundred of thousands of bitcoins and he is very happy about that.
Personally, I think he'll come back in couple of years.
At that point, bitcoin will be widely used, and buying stuff with bitcoin
would be as easy as buying with fiat.
So, he will USE his coins.
But since when does using bitcoins means exchanging with fiat?
He will just buy stuff. Nothing more.
Also, who knows that Sathoshi isn't already using bitcoin?
We can't be sure we know every Satoshi's wallet address.
He may have a secret 100 btc wallet, and living from it
I have exactly the same opinion about Satoshi and his Bitcoins and I wrote it before, but you've explained it perfectly.