Does the system need to re-create those money?
One of the primary advantages of Bitcoin is that "the system" will never create more than 21 Million coins. This preserves the supply available and therefore the value of Bitcoin. Today's fiat-based currencies are managed in the opposite way, where Central Banks print more money as they need to to control (and manipulate) the value of a currency compared to others. This "need" is done to allow a Countries goods to remain affordable for other Countries, so exports remain high and income and GDP remain high.
What this also does is erode the value of the fiat currency, which is why prices for goods and services increase even though it's easier to produce the good/service.
There are thousands people lose their private keys every day. And it does not effect in Bitcoin value. Besides, those Bitcoin can not be used because no one know the private keys.
Wrong, it absolutely affects the Bitcoin value. With fewer coins available to be sold the price of bitcoin stays higher than it would if no coins were ever lost.