Thanks for the replies.
I still don't know if it makes sense to hang onto it until about 300000km or not. I really like the diesel the way it cruises up hills and with the good fuel economy it gets. I think it is paid for in a month or two and I will find out what they will give me for it.
FWIW, the 1.8 TSI gets pretty decent fuel economy if you don't beat up too hard on it. With 185 lb-ft of torque with 5-speed manual, or 199 with automatic or 6-speed manual 4MOTION, starting at 1500 RPM, it scoots up hills pretty well too.
With the slightly shorter gearing of the 5 speed's final ratio, I find my '16 Golf and my wife's '17 Golf Sportwagen go up hills just as competently as our TDIs did. There are hills around here where I can blast up in top gear in my TSI (5th gear) that required, on my TDI, a downshift from 6th to 5th.
On the flip side, the extended warranty if you take the fix, for the emissions parts (which I think includes the troublesome HPFP) and the cash might make hanging on attractive.
For my wife it wasn't worth it, the delta between the VW payout and the cost of a new car was only $3k before tax. We got a brand new car with the warranty reset to zero. Most of the year here diesel runs from well above RUG (in winter) to just slightly below (summer) so the cost of RUG is marginally lower on average all year, and the cost per km not much different compared to our previous TDIs.
Plus the TSI is way smoother and quieter than a TDI.
In summer, on my Golf hatch, I average 5.8 L/100 km compared to about 4.8-5 on my Mk VI TDI. My wife's wagon averages closer to 6-6.4 under the same conditions (we both drive mostly on rural roads).