It would be great if we can investigate this issue with a save file where this offer is not yet sent.
Sadly I don't believe I have one, and most recent save is one after I conquered all of the land.
I'll look when I get home but most recent save prior is probably waaaaaaaay earlier in the game. Granted I don't know how auto saves work, maybe one of them is ok. Although I've started two new campaigns since then so they're probably saved over by those.