Impressive!
If someone were to ask you "How much longer do you think it will last?", I suspect your answer will be "It's still too early to tell."
I've had people ask me that after my 02 Golf had over 300k miles on it.
How long will a properly maintained TDI last? The world may never know.....
Be sure to watch the odometer for when it rolls to exactly 444,000 miles. Reset the trip meter at exactly 444,000 miles. Then take a pic of the display when it shows 444,444 miles on the odometer and 444.4 miles on the trip meter.
Be watching and ready for that moment when it arrives. I did that when my 02 Golf TDI reached 333,333 miles and 333.3 miles on the trip meter (sold the 02 Golf in 2010 with "only" 361k miles on it).
Sorry for the poor quality pic. It was taken at night with the instrument cluster brightness turned down to avoid saturating my cell phone's camera.
Good luck.