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.
That would depend in the terms specified in the contract. If the entirety of the contract is the email message which says "We'll pay 10K for a referral that lasts 6 months", then it defaults to the contract laws in their state. I can guarantee that the contract laws of their state do not say "debts owed to employees are void after employment is terminated."
> How long is he allowed he wait? 10 years? 100 years?
Most, probably all, states also have a law defining what the limit on collecting a debt is. It usually falls between 3 and 6 years, and is considerably longer in a few.