I got a 2015 TDI Jetta in May of 2015. It gets wonderful mileage when I'm on the highway. 51-52mpg on long hauls on the interstate with cruise control set. I'm

I got a 2015 TDI Jetta in May of 2015. It gets wonderful mileage when I'm on the highway. 51-52mpg on long hauls on the interstate with cruise control set. I'm honestly torn between taking the total amount of money or the $5,100 and letting them fix the car. I just hope it doesn't kill the fuel economy too much. ...and what downsides are there to holding on to the car if they have a fix?