There is no other contingency for charging to dining plans. The POS systems at the restaurants have to charge something. I'd like to hear any ideas if you have any.
And there we have the EXACT problem here. I am usually the last one to call foul on Disney, and quite often I tell people stuff isn't as big a deal as they may think, but this is a huge deal for a myriad of reasons.
If this system has been in development for a decade as you say, then it was ______-poor planning not to have some sort of plan for if something like this happens.
I work for a company on the Forbes 100 who works with millions of financial transactions across dozens of systems every day. You are absolutely right - downtime happens. Especially when you are making a wholesale change to the system.
HOWEVER, it's my company's responsibility (and Disney's, in this case) to make this as PAINLESS to the customer as possible by HAVING contingency plans.
I know that in the Disney-bubble people who work there are trained to think that each shop, restaurant, etc. is it's own financial entity, which on some cases it is WITHIN WDW. But it's still all owned and run by Disney for the most part, and even the places that aren't (like in WS) they still use Disney terminals/etc.
You know what happens at my work (who deals with just as many, if not more, customers per day than Disney)? We pull out sheets of paper and start writin' stuff down. We do what it takes to keep the customer experience, get them on their way, and we deal with it all later. If we lose some cash in the process, it's on us - the customer gets taken care of.
In this case, there are about a dozen different methods they could use. Just because they can't run it through the machine doesn't mean the entire place is frozen up. They could have issued emergency "coupons" (you know, little pieces of paper, like before everything had to be on a card?) at the hotels, they could have kept manual track of them at the restaurant and reconciled them later (and if people ended up with extra free meals, hey, that's the price the company pays for downtime, anticipated or not), they could have set up a mini-call center for restaurants to verify things at, any number of things could have been done.
I'll tell you why this peeves me - it's because many families couldn't afford to do what the OP is doing. I help a LOT of people plan Disney trips, many of whom never dreamed they could afford to go. Families spend years saving for a one-week trip. And many that do the dining plan do so because they want to have a fixed-food cost so they don't have to worry about that during the trip. Not everyone has some AMEX Platinum card without a limit they can just throw stuff on. I know families that, if this happened to them, and they were "trapped" on Disney property without a car, they'd be hard pressed to be able to afford to spend $100's extra on food they hadn't anticipated (even if it gets reembursed later).
So, big bad on Disney for this one. We all know system outages and updates/upgrades happen and can go wonky, but that is DISNEY'S problem, not the guest. Disney should have done whatever they needed to and given people out the food they had paid for without making them pay their own $$ in advance. It's great they FINALLY let people put them on room charges, but it's pretty inexcusable that it took as long as it did.
To anyone who thinks, "Oh this is no big deal, if you can't afford a few extra meals you can't afford to go to Disney", I ask them to think about the 5-year old with them who's dreams the parents scraped money together to be able to make come true, and how not everyone is in a financial position to come up with $100's of extra dollars with no notice when they had already paid for the meals in advance.