I'm so sorry about your DH's job.

I wouldn't make a decision yet. I'd wait until closer to the date to pay the package off (45 days before your trip). I'd be considering the following:
What does your DH plan to do after the end of the year? What are the prospects? Will you have to relocate? If he finds another job before the end of the year, what does that do to any severance or benefits he might get from GM?
Do you have an emergency fund? How many months can you survive on that money?
What happens to your health insurance at the end of the year? Is it covered by GM for awhile, or do you need to get private insurance or COBRA (likely WAY more money than you are paying now)?
Can you get a credit from the airlines? Will your DH be looking for a job outside your area where that credit might come in handy (if not for job hunting, then for house hunting if you decide to move)?
If you do have to move, how quickly can you sell your house? Can you afford to pay your mortgage (if you have one) plus pay for a place for your DH to live in the new area?
While your trip is relatively inexpensive for a Disney trip, the $1200 you haven't paid yet might make a mortgage payment or two or pay a month or two of health insurance. It depends on the state of your finances. You might be out $900 if you don't go, but you will be out $2100 if you do go. You will have a wonderful trip to show for it, but it won't pay the bills.
Best of luck in your decision and with your DH's job search.