Part of the issue is that demand wasn't high for the last few Disney films before Frozen. We are talking Planes, Monsters U, Wreck-It Ralph, and Brave. Merchandise was easy to find and a lot of stuff ended up on clearance. It just wasn't selling. I remember when Brave came out and all the stuff that was in the stores for it... and it just did not sell.
So, you are Disney's merchandising department and you have to decide how much to purchase and have made. If you look at the historical numbers, you see "low" sales from those movies. So, do you ignore history and risk over purchasing and losing money? Or do you take those numbers into account and lower your purchasing amounts?
Most companies would do the second. It makes sense and is totally logical from a business standpoint. It is the decision I would have made.
The problem is that, instead of following the trend, you ended up with a hit beyond anyone's imagination. Now you don't have enough merchandise to meet the demand. Scarcity also increased demand because of the idea of "If it is this popular, then I NEED to have it." Disney has been ordering more merchandise, but it takes time. It's not like they just call up and it appears in the numbers they want. It appears they are doing multiple smaller shipments to try and get the items out there as soon as they are ready (which is more expensive for them) instead of waiting for a larger amount and doing one shipment.
I doubt "heads will roll" because of the decision made. You can't see into the future. You can only use the information you HAVE to predict what might happen. This is called a forecasting model. The data suggested ordering less merchandise based off of historical sales for past movies. I am not sure how anyone could expect them to have realized, before the movie was even finished (as ordering merchandise is done way ahead), that this movie would be SO different.