He made very big mistake but there is no information like is it a wallet that stores all of his fund. If it is like this, it is truly nightmare for him.

He and any other people knew about this accident, will need to learn from this and reconsider how to back up their wallets more safely and more privately. This is a good guide on how to do that.

How to back up a wallet seed phrase ? (Jameson Lopp).

Very important rules:
Don't store all fund in one wallet as it is like store all eggs in one basket.
Don't bring that big wallet around everywhere as you can have problems and lose it as well as all your fund.
Don't try to split your wallet seed phrase.