if the private key does not shine anywhere, then you will be safe. because in 99% of cases, hacking occurs on the vein of coin holders. manual hack wallet is not possible
Manual hacking by making random private key will only direct it to a random eth wallet, same as guessing an user password. It's almost impossible to do to get it to the right eth wallet. It will take a very long time, I think it will spend all of its age.