It's not enough to do a rewrite. Someone has to maintain it. Such a huge codebase with literally zero experts is unmaintainable. There is no one who knows how the internals work.

Sure you could keep vibe coding it but I wouldn't bet my data on that. A database needs to be rock solid.

This seems to be the issue with using LLMs for any code generation. Even with my own code bases that I've written entirely by hand over years, if I use AI to implement anything, I don't go through the mental model of architecting it, so I don't know how it works. I can only imagine this to be far, far worse for large code bases maintained by a team of people who are all using AI.