Nah, there's no legal force behind the pledge. It was always just a pinky swear.

It stopped giving the wealthy so much positive PR so a lot of them have simply stopped talking about it. Whether or not they still go through with it, who knows. I somewhat doubt they will.

The other problem people are quickly becoming aware of is that charities are ineffective ways to solve social problems. And, particularly for very wealthy and well connected people, the charities seem to be much more of a tax dodge with a glossy pamphlet rather than anything real.