I'd say it's more than a bit too soon to say that Vulkan is dead based on Apple not implementing support in an OS that comes out this fall when the first drivers available to consumers elsewhere probably won't be available until after that. Besides, drivers are being written for both Windows and Linux at the moment and I wouldn't be the least bit surprised if Apple was at least having a look at Valve's open source reference drivers while preparing to have Vulkan and OpenCL 2.0 drivers in next year's release of OSX.
Apple won't kill ether OpenGL or OpenCL support, or if they do that it'll obviously be with a similar time table to how they killed support for PPC binaries. Too many applications use the two API's. With OpenGL it's not just games that use it, it's heavily used by CAD/CAM, 3D modelling, image editing, graphical design and pretty much any software that involves the user drawing or otherwise creating complex shapes on screen. While some companies may be persuaded to switch to Metal, there's too much invested in software built around OpenGL for us to see a phasing out of OpenGL until maybe 5-6 years down the line.
That's a user point of view. But I'm a developer. So, from my point of view, an API that gets cornered into compatibility/support status is a dead API, because in the mid-term you won't be able to use it for accessing the latest hardware features. In that context, what Apple is saying today is that OpenGL and OpenCL are dead (in other words, if some future GPU supports any new feature, you can expect it implemented in Metal, not in OpenGL nor OpenCL).
A very disappointing bit about this are the users who purchased a new Mac Pro. An expensive machine, theoretically optimized for OpenCL, with expensive dual GPUs, whose degree of support under Metal is still uncertain. I'm glad I decided to wait for later generations of the Mac Pro, when the new strategies from Apple get clearer.
Regarding Vulkan, it's still unborn, just preliminary implementations, but we see Microsoft pushing for DX, and now Apple pushing for Metal. Who's going to push for Vulkan? And it didn't arrive to a public status yet.
I've read very good reviews of the internal design of Metal, although didn't use it myself yet. If it's such a good API, maybe a good approach could be to write a compatibility layer from Metal to other OSs APIs (if that's feasible to some level), and write everything in Metal.
Because I develop for Mac, but also for other OSs. I know Apple wants us to target Apple products only, and the new API strategies from Apple clearly show their will, but sorry Apple, we'll still develop for other OSs too (you know, no OS stays forever, and well designed software surpases OSs lifetime).