It's still risky because he has to trust the guy in the customer service for this. The best shot for him is by any chance if he has the 12/24 word seed then he can restore the wallet using Electrum. But he has to have the seed.
The old version seeds aren't BIP39 compliant since it was years before BIP39.
All he can do with it is to use the legacy recovery page "
forgot password" to get his (
missing) wallet ID and password.
Even if it's years ago, as the quoted email said, their customer service may help if you can provide enough proof of ownership (minus the password).
But what kind of proof does OP have? Does list of bitcoin address and rough date when the wallet is created/last serve as valid proof?
Some people were asked for wallet creation date, known used IP address(es) which IMO, not enough proof.
But since he'll just ask for the Wallet ID which is useless without the password, I guess blockchain(com) may consider.