Nothing in his post suggests the ERP's DB is gone, merely that the mechanism which populates DNS records from the ERP has broken down, which probably has ripple effects on everything else as their internal DNS is broken and services can't talk to each other.
But the data should still be there, and it's a matter of reverse-engineering how to go from "ERP DB" to "DNS zone file".
> Skimmed through the MySQL and Postgres databases, no signs of anything domain-related. I'm betting it's all stored in the custom integrated [and encrypted] KV database..
It doesn't, but in my experience, the ciphers and key sizes commonly used were often not future-proof :). This rests on the assumption that nobody updated the keys/encryption components in 20 years - which I think is quite possible with such internal enterprise deployment.
But the data should still be there, and it's a matter of reverse-engineering how to go from "ERP DB" to "DNS zone file".