OpenGL 4.5 Is Not The End Of The Road For OpenGL
The Khronos Group has publicly stated (as well as in past briefings with their representatives) that OpenGL will continue to co-exist with Vulkan. Khronos isn't going to immediately toss out the OpenGL specification and leave it to rot once Vulkan 1.0 has been announced. There is almost definitely going to be an OpenGL 4.6 or maybe even at some point OpenGL 5.0.
OpenGL is still expected to gain functionality for Vulkan integration / being able to load SPIR-V on supported drivers/hardware. Other additions to OpenGL are still possible as well by interested parties. Even after Vulkan was announced last year, new OpenGL extensions were still baking. OpenGL is not dead.
There are going to be millions of graphics processors out there still relying upon OpenGL as they don't meet the GL 4.1 / OpenGL ES 3.1 hardware base requirements for Vulkan. There is also going to still be countless OpenGL applications in the wild for the foreseeable future from legacy software to game renderers that likely won't be ported to Vulkan for seeing little return on investment by the smaller studios. OpenGL may also still appeal to new developers for not needing a graphics API as low-level as Vulkan. OpenGL is also still expected to be used in some embedded cases too.
It's also unlikely that the commercial application vendors (think CAD software, etc) -- which drive much of the longtime Linux OpenGL commercial interest and are the big NVIDIA/AMD Linux customers with direct lines of feedback to them -- will risk quickly switching over to Vulkan. In cases like 3D medical imaging and other sensitive fields, there are also other huge implications and headaches involved.
At least for a long while, OpenGL will continue to coexist with Vulkan. OpenGL is not dead. Another pet peeve has been how some thing Vulkan is going to make the Linux gaming market-share quickly shoot sky-high. Yes, Vulkan will help modern game engines on Linux better compete performance-wise with Windows, but how does that help the number of usability problems with Linux for traditional Windows users and how does it suddenly make Linux any more appealing than Windows for such gamers when they too will have Vulkan to complement their Direct3D 12 support? Vulkan is great and will allow the potential for much better performance and better quality cross-platform software, but it's not a magic bullet.