Well, this is one of the major risks associated with using bitcoin. With a simple mistake, one can lose all in a twinkle of an eye. One of the most effective precautive measures in keep your bitcoin safe is to keep your wallet keys as safe as possible. One method I employed is to make copies of each of my wallet keys and keep them safe. That way, I can always recover it even if one got lost or missing.
I sincerely do hope he is able to recover the coins because that's a whole lot of money to lose .
That's why I asked recently in a thread I created about
additional security measures. If I had the equivalent of $1M in Bitcoin, I wouldn't have it all in one place. It would be better to have like 3 wallets, with their seeds written and well stored, all stored in different places, the hardware wallets and the seeds, and maybe something else.