It's hard to say what will happen at the airport as I suspect each airport has its own procedure for departing passengers. The airports I have flown out of lately don't have a passport control for outbound passengers - it's all handled by the desk personnel at the airline's check-in desk.

It also may depend on what state his passport is in. If he came in on the visa waiver program, there should still be a little green slip attached to his passport. Normally, the desk agent simply retrieves this to send to the immigration people to alert them that he has left. Whether the agent checks the date on it or would do anything if he or she notices that he is well past his "sell-by" date is anyone's guess.

If he doesn't have the VWP receipt to turn in, I don't know what the protocol is. But the fact of not having turned in the departure slip at all is probably more "serious" than turning it in late.

As far as how long you'll have to wait before applying for your fiancé visa, I don't know. If I understand the requirements correctly, he'll have to show that he can support you (living with his parents or not) so I suppose it would be best if you waited until he starts a new job.

In any event, good luck.
Cheers,
Bev