Has anyone had experience/success interacting directly with Google on similar issues to recover past/ongoing correspondence and records?
To head off the early questions:
1. Yes, we worked hard to prevent this situation, but we're in it now.
2. Yes, we have extensive legal support/advice.
For example, you could demand the emails, as a part of "returning company property." If they don't, you might be able to pursue legal action, that would entitle you to discovery.
And if they refused, maybe you didn't offer enough?