This is in regards to your query posted on the website CarDekho.com, we would like to inform you that Maruti Swift VDi gives mileage of 14.2 kmpl in city conditions and 17.8 kmpl on highways whereas, Maruti Ritz VDi gives mileage of 17.7 kmpl in city conditions and 21.1 kmpl on highways. Both the cars are powered by same 1248 cc petrol engine but Maruti Ritz Vdi churns maximum torque of 113 Nm at 4500 rpm whereas Maruti Swift Vdi churns torque of 190 Nm at 2000 rpm. The interior space of Maruti Swift is more than Maruti Ritz.
You can use the given link to Compare Maruti Ritz VDi and Maruti Swift VDi.
Maruti has a good and vast service network and there will be no problem of maintenance and replacement of parts at later stage but the resale value of the car might decrease as the company has decided to discontinue the vehicle. Despite this, there will never be any shortage of parts as manufacturers make parts for next 10 years. Also, as Ritz share a good number of parts with its sibling Swift there will be no shortage whatsoever. If you would like to consider, the Indian auto market has many other offerings in the same segment such as Tata Bolt, Nissan Micra, Ford Figo, Honda Brio and Grand i10, Maruti Swift, Chevrolet Sail hatchback.