How much of the vas deferens would constitute too much removed, to be able to have a vasectomy reversal?

Vas reversal: Successful fertility after vas reversal depends on many factors. Length excised is usually not well documented. A more identifiable determinant would be length of time since vasectomy. The greater the number of years, the less the success. At best, the success rate rarely is above 50% (using pregnancy as the determinat of "success").