i dont know how long the engine can last, but my car's engine shows absolutely NO sign of being near its end even with 220,000kms mileage. and that too, kept on CNG... BUT i follow the maintainence schedule strictly... my guess is i ll get to 300,000kms mark easily on this engine without any reducing oil issues etc. and almost twice that if it was done on petrol... all depends on how u maintain a car, no car in the world can go on without proper maintainence for long...
Someone i know had to change the idsi engine at just 126,000kms... because of how the engine was treated...