This. I've done this with RUCs several times, even recently. GUCs are obiouvlsy different but it really comes down to the agent you get. It's worth calling and trying to book something before they actually expire, then they are truly wasted. Your odds of using the GUCs after expiration with a trip purchased now are much greater than Delta agreeing to further extend their expiration.

And if they do expire, take comfort that international J hasn't been that great with all the catering cuts. Here is a trip report from when I used my last GUCs on KLM back in July.