The problem with having their entire market dependent on Intel is that Intel is about to do the same thing AMD just did, that is integrate a GPU into the CPU. Once Intel does that the entire low end market is absolutely gone. Whether there is a sustainable market for discrete GPU once the low and middle are taken over by the APU is a very valid question.
People need to keep in mind a little history here. The industry moves in cycles, CPU’s tend to cycle to slowly for fast moving technology but as the rate of advancement slows that technology will get reintegrated into the CPU. Shortly before 3D cards became popular discrete graphics cards cratered in price. There was little to differentiate them and there was talk of integrating their limited circuitry into the CPU. Once 3D hit the 3D tech was moving at 4x the speed of the CPU refreshes so discrete parts became the norm, but we will cycle back to integrating the circuitry back into the CPU, it is inevitable. We are rapidly nearing that point, GPU refreshes are nearly every 2 years at this point, which is the same as the CPU cycle making it economical for the CPU vendors to integrate the GPU’s onto the die. There will undoubtedly be a discrete market for a few more years to come, particularly if they come out with a new technology that everyone needs. I’m not optimistic that will occur and without the huge sales of the cheap parts I’m doubtful that companies like nVidia can sustain the R&D machine to compete with the CPU makers.
nVidia isn’t going to be gone in a year, or probably even two, but I doubt they will survive the decade. I actually see them being sold to Intel in a few years.