If NVIDIA exits the market, there is still AMD, Intel and PowerVR (Imagination Technologies is back at making discrete PC GPUs, although currently only in China).
In the latter case, I'd expect patches for AMD or Intel to become a priority pretty quickly. After all, they need their products to run on systems that customers can buy.
Intel is just plain not capable of it because it's not really a GPU, more a framebuffer with a clever blitter.