Road Condition: 450km Karachi-Nagarparkar
Karachi to Nagarparkar road has not only improved a great deal, as compared to when I last visited in 2013, but the shorter route through Badin is also fully functional now, courtesy full swing development work at Thar Coal Mines near Islamkot city. The new route has cut down the travel time by 2-3 hours from the previously preferred, but longer, route through Hyderabad, Mirpur Khas, and Nuakot.
Karachi-Maklli-Sajawal-Badin
We first took Karachi-Makli National Highway and turned right just before Makli city, through bypass, towards Sajawal and Badin. This part of the National Highway, ~100km, and beyond, is recently renovated as a dual carriage and has thus transformed into an excellent drive.
The single carriage Makli-Sajawal-Badin road, a little over 100km, is also in good shape with bypasses circumventing most of the enroute bigger towns and cities, making it a comfortable drive. 
Badin-Mithi-Islamkot-Nagarparkar
Badin-Mithi is another 100km or so single carriage pleasant drive, which meets the Mirpurkhas-Naukot-Mithi road near Mithi. The smooth road then passes through Islamkot town before crossing Thar Coal Mines Turn, named Engro Morr, 50km from Mithi.
After crossing Engor Morr, the road towards Nagarparkar, another 80km, gets worse, with potholes and withered sides, making it not only uncomfortable but also risky to drive. Hope this part of the indigenous local population will also get some fruits of development in the near future.
Overall, it was a good driving experience and took 9 hours, in total, one way. with a couple of extended stops. On the return, it took around 8 hours due to brief stops, which is conveniently and safely doable without over-speeding. 
Nagarparkar to India-Pakistan Border (Choorio Village), 40km mostly off-road
The visit to India-Pakistan border till Jog Maya Mandir at Choorio Village is possible through 4x4, which can be hired from Nagarparkar Bazaar. We went with Ramesh, 03412267900 and paid him Rs. 3,000. Recommended. It was one and a half hour tough ride, as compared to Karachi-Nagarparkar pleasant drive. It can get really hot during the day so keeping drinking water, which is scarce there, will be wise. Round trip will cost around Rs. 3000-4000.
Caution: Cattle Crossing
Cattle crossing - sheep, goats, cows, and camels - is a common occurrence around Thar roads and require driver vigilance. A friend who recently visited Nagarparkar with a group met an accident, in the night, when their hi-ace windscreen smashed with the head of peeking camel. So night driving is not recommended in this area. Another fellow traveler also reported hitting a sheep, in the daylight, thankfully without any damage.