If some people has lots of bitcoin in their offline wallets and they die or lose memory.
Then those coins will be out of circulation right? Or is there any way to recover them?
yes definitely the bitcoin is lost forever if the private key or password of deceased person isn't passed to someone or forgot to pass it. that's why we should be prepared them in case of amnesia oe worst death they could move the bitcoins so they can use it. well incase of wallet.dat corruption well we have nothing to do just cry..
This is why private keys should be keep because once it will lost it will lost forever. This is the importance of our private details to kept it. Because there is no other way to recover them.