Oh man I feel sorry for that guy. It’s really important to be super extra careful of the things that we store and delete like the private keys. This is why I am very sensitive to some stuff especially when storing these keys offline (and some on my Protonmail account where I’ve also secured my password).
Storing them offline is still the best option.
Really pity on losing a huge money. He could've saved the private keys on different locations. Being into the mining process from the age of 14 is big thing and this knowledge could've kept him well aware of the security system of bitcoin network.
Right now only option is to request help with recovery service providers. But we can't expect positive chances on recovering the funds. Maybe this is his fate, so we can't change the situation only God has got the answer for this.