Abandonment is a risk facing any heavy "all-or-nothing" frameworks, not only is this bad for existing apps built on YUI, but it's also bad for developers skill set investments that will soon become obsolete.
It's hard to imagine heavy popular frameworks like AngularJS falling to the same fate, it would need something far superior with a lot of traction to displace it. But it's still a risk if you build your application the "Angular Way", "The React Way" or "The Ember Way", etc where if the primary developers halt development for whatever reason, your app dev stack becomes obsolete making it harder to attract great devs (who don't want to invest in a dying platform).
It's less of a risk with lightweight frameworks and libraries like Backbone.js where the code-base is so small and extensible, anyone can easily maintain their own fork. It's also less of a risk for WebComponents as the component model leverages the browsers DOM and lets you use modularized encapsulated components built with different technologies, so if one of the technologies ever becomes obsolete you can always start writing new components with newer tech and integrate it with your existing app, without having to rewrite it.
It's hard to imagine heavy popular frameworks like AngularJS falling to the same fate, it would need something far superior with a lot of traction to displace it. But it's still a risk if you build your application the "Angular Way", "The React Way" or "The Ember Way", etc where if the primary developers halt development for whatever reason, your app dev stack becomes obsolete making it harder to attract great devs (who don't want to invest in a dying platform).
It's less of a risk with lightweight frameworks and libraries like Backbone.js where the code-base is so small and extensible, anyone can easily maintain their own fork. It's also less of a risk for WebComponents as the component model leverages the browsers DOM and lets you use modularized encapsulated components built with different technologies, so if one of the technologies ever becomes obsolete you can always start writing new components with newer tech and integrate it with your existing app, without having to rewrite it.