I own the pre-VR 300/2.8 Nikkor and had it repaired just one year ago. Thus, if you are lucky, spare parts will be available for much longer than the standard 10 years. However, as Ilkka points out, predicting the failure rates of components in the future is not simple, and some parts might well run out of stock even before the grace repair period is elapsed.
If one should increase the odds of having a functional lens for a life-time, getting a purely manual lens is the wiser option. Or just buy your dream lens now, use it, and worry later.