I don't know for certain that you cannot purchase it at this late of a date, but I'm fairly certain you cannot. With all the weather lately, it's possible that Disney may loosen the restrictions. Your best bet is to call and ask.
I'm not sure anyone can tell you to do it or not do it, especially if it seems it will be a very tight fit for your family. The odds of a complete shut-down are slim, but it's always possible. How badly would it affect your vacation if you lost a day or two to weather? Anything more than that seems very rare.
It seems from all the recent posts that everyone has had a great time despite the storms around Orlando. Unless there is an actual hurricane (which I know is always possible), it seems Disney World manages to still be enjoyable with crappy weather.
I've been told by cast members that Disney is one of the safest places to be in the Orlando area if a hurricane happens. They claim that some people will actually book rooms there if a hurricane is actually going to hit the area. So much of Disney is self-contained, that they can manage to function fairly well handling the hotels, food, power, and even medical emergencies. I know I've seen other posts about Disney being one of the few places to receive a status of safety...which I cannot remember the name of.
I'm fairly certain from what I was told when I declined my
trip insurance for next week that you cannot purchase it later....I took that to mean once the trip is paid in full. That being said, it means you cannot purchase their trip insurance afterwards...but you may have luck purchasing through other venues if you are worried......such as your home or auto insurance company.
For instance, when you purchase a car they will sometimes try to sell you "gap" insurance...which covers the gap between what you've financed, and what the insurance company will cover if your car is a total loss. It's usually several hundred dollars, and they typically try to convince you to finance it so you only pay a few extra dollars a month.....and you cannot purchase it after you leave the finance office. This is it, your one chance to get it. Truth be told, you can probably purchase the same insurance from your auto insurer. We asked our Nationwide agent and she informed us that they would charge fifteen dollars a year to add that insurance for us.
You may be able to find trip insurance elsewhere if you can no longer get it from Disney. Lots of people like the safety of having it for emergencies, and lots of people decline it and turn out fine too. It's really a very personal decision. If all those involved are old enough, and wouldn't get scared talking about it, maybe you should have a little family meeting and run some scenarios to find out how much bad weather would affect everyone in your group.
I hope you have great weather and no worries!