> At that point it became a debt that the company owed jzhwu
I considered this, too. Obviously I agree that, if it were a debt, then he is entitled to it, and that the debt cannot disappear.
But what if it's not a debt? I think that the debt exists if the creditor makes a claim. Perhaps by not asking for his bonus, the employee lost his opportunity to make a claim, and cannot make a claim after resigning.
Your suggest he claim the debt at any time. How long is he allowed he wait? 10 years? 100 years?
All I'm asking is that you see how this could be argued either way! Obviously a court (or case law) would decide one way or another, but until that point it is ambiguous.