I was just talking in class today about how people want to back-breed aurochsen out of extinction. Here's a new story about the idea, from the Telegraph:
"We were able to analyse auroch DNA from preserved bone material and create a rough map of its genome that should allow us to breed animals nearly identical to aurochs," said team leader Donato Matassino, head of the Consortium for Experimental Biotechnology in Benevento, in the southern Campania region.
"We've already made our first round of crosses between three breeds native to Britain, Spain and Italy. Now we just have to wait and see how the calves turn out."
But I wouldn't rule out the possibility of back-breeding the genetics to look reasonably like some wild aurochsen. Old breeds were selected for diverse things, but most of this selection would have used standing variation initially. Few new mutations would have fixed in the time since domestication, and if one fixed in a single breed, it would have been unlikely to have been introduced into other old breeds until recently.