I think the WTS will be okay. They're in the middle of a reorganization right now due to the decline of paper literature and donations, but they'll adjust. They should be able to survive off real estate investments and whatever their future donation stream is.
My prediction is that once tablets are ubiquitous and cheap enough most publishers will transition to digital publications. This will save the WTS a ton of money. Imagine how expensive it is to print and ship literature around the world. Heck, the new Amazon tablet just announced will be $199.
Selling magazines door-to-door is also becoming archaic (not to mention expensive), so perhaps they will encourage publishers to focus on just using the Bible and a tract that points people to the official website if they want to download magazines or get more information. Most people do that now anyways so this should be an easy transition.
The only way I see an implosion is if there some sort of huge scandal that gets a lot of press. It would have to involve high-ranking WTS officials or GB members and be something really outrageous, like a child porn ring, a Bernie Madoff-sized ponzi scheme, or something crazy like that.