It is widely believed that the blackbuck became extinct locally in Kanha due to hunting and poaching coupled with habitat loss & habitat degradation. When the wildlife populations get miserably low (to few individuals), the chances of recovery are bleak and they get locally extinct however resilient as a species they may be quotes some studies including John Seidensticker's on Sumatran Tigers.

The habitat degradation due to plantations and proliferation of invasive have also bothered black bucks largely in many of their range.

Perhaps the only place in India where black buck and tiger are found together at present is Sathyamangalam (not sure about black buck status in Nagarjuna Sagar Srisailam TR).

Thanks for sharing your valuable insight gained out of rich experience.