I’m not sure he’d want to, it would seem like he might want to point to his own scam. But if he did, I imagine he could add back your TXT record after looking it up in any of a large number of historical DNS databases. I can’t vouch for the quality, but a casual Google suggests there are still many, primarily paid but some free-ish, in the mix. Examples:
https://whoisfreaks.com/tools/dns/history/lookup
I really don’t think a TXT record is a good place to keep a secret… although it is a good place to prove you control a domain.