Yes, but it's not forever... In dozens of years big computers will be able to break the encryption and find the private keys of these accounts. Maybe before 2047....
After, all 21 million bitcoins have been extracted and the bitcoin rate will rise to incredible heights, it can be extracted from the block chains by selecting the cipher to the closed keys and the previously lost bitcoins? It will be something like a new kind of mining. However, apparently, this occupation will be worth it, given the course of bitcoin at that time.
incredible heights... I don't know. It's likely to not be number one anymore in few years... maybe months