Op is correct that it's hard to evaluate the number of lost coins, since we don't know why some wallets are inactive. I think of them as just inactive, and I don't view them as lost forever.
As for Satoshi's coins, we shouldn't focus on someone else's money.
Bitcoin is scarce by design, which will drive its price up if more and more people want to get some of it. But, thankfully, each Bitcoin is divisible into 100 million satoshis, so we can actually just refer to satoshis rather than bitcoins in the future if the price becomes that high and satoshis become a more relevant indicator of prices. So the issue is not as serious as it might seem at first glance, even if a significant part of coins is lost.