Although I agree it's a terrible decision for Apple only to have Apple-specific graphics APIs, please note that:
* Being deprecated does not mean that things will suddenly stop working. It will take a few more releases of macOS before this can be removed.
* Next to MoltenVK there is MoltenGL, which is an implementation of OpenGL ES 2.0 that runs on (edit) Metal [1]. That indicates it's at least feasible to wrap OpenGL applications in the future if necessary.
Furthermore, Apple wil drop support for all Macs that don't support Vulkan in this release of macOS [2]. Ouch, what a waste.
* Being deprecated does not mean that things will suddenly stop working. It will take a few more releases of macOS before this can be removed.
* Next to MoltenVK there is MoltenGL, which is an implementation of OpenGL ES 2.0 that runs on (edit) Metal [1]. That indicates it's at least feasible to wrap OpenGL applications in the future if necessary.
Furthermore, Apple wil drop support for all Macs that don't support Vulkan in this release of macOS [2]. Ouch, what a waste.
[1]: https://moltengl.com/moltengl/
[2]: https://9to5mac.com/2018/06/04/macos-10-14-mojave-supported-... (anything from before 2012 does not support Vulkan)