Why would anyone say that? Sketch is still alive and (presumably) well. Apple themselves continue to officially release design files for Sketch with every OS release. They share more resources for Sketch than any other app, including Figma and Photoshop.
http://developer.apple.com/design/resources/
> after they depreciated Fireworks
I’ve been seeing that word used a lot in this context, so just wanted to point out (I’d appreciate if someone did the same for me) that what you mean is “deprecated” (no “i”), as depreciating is a different thing.