I think many people have misconceptions about the diesels. Modern diesels are lot more efficient and environmentally friendly than gasolines. You can see the details in Mercedes BluTec for example.
The 1.4 D4D (1ND-TV) engine is long due for Pakistan, and offers a very good combination of power and economy. 26 KM/L is not even offered by new Prius (or used imported Prius). Someone said diesel is costly? Well an average of 26 would vastly offset 10-12 rupees higher cost of diesel. It will eliminate the need for CNG.
Now coming over to maintenance, new diesels are almost maintenance free. I have a diesel car and I change oil at 5000 KM and its as new as the day i bought it, only downside is that you should not use 3rd party filters like Guard etc. Other than that no maintenance is required.
D4D engines have a Common Rail Injection system which is under very high pressure (25000 psi). The injectors are sensitive to impurities in fuel but that applies more to particulate contamination and water and less to sulphur. With some extra care, D4Ds work equally good in Pakistan. You see so many D4D Vigo and Prados.