There don't appear to be any bulldozers . . .
So, let's say that WDW grosses about $400 million a year in operating income. That's profit to throw into the vault. Let's say that Uni's Potterland 2.0 brings in more guests into Orlando, maybe Disney's profits falls a bit, but they are still pulling in $375 million, heck it might go up given that you have more guests coming into Orlando.
Realize that they could make WDW's yearly profit off of one Star Wars film. Realize that they are looking at expanding into emerging markets. Realize that NFL is greatly needed guest capacity, and that Avatarland will draw in folks, perhaps folks who aren't Potter fans.
In the end this whole, "Disney has to do this or they'll be toast!", is just hyperbole from fans who want something new immediately and can't wait 4-5 years.