Just asking if anyone's had drivetrain work denied following remap/box use and subsequent removal isn't going to prove there isn't a way for VW to detect if you don't get a response.
The most likely negative outcome for a remapped car is a slipping manual clutch. If you get one of them beyond 30k miles (and perhaps before then) is that it's a wear and tear item. My stock R slipped its clutch a few times at 23k miles in the coldest weather we had, and I couldn't replicate it to persuade the dealership to do any investigative work on it.
I've had 10 VWs from new and VW seem to be going out of their way to avoid responsibility for warranty work on technicalities, as I recently found out with a request to fix my tailgate, part of the work was to adjust the striker plate that had been badly fitted at the factory, with the tailgate requiring a slam to close. Warranty denied because there's a sneaky 6500 miles/6 month clause on adjustments - I was 7 months and 5800 miles since new.
Ended up fixing myself. The warranty manager of the dealership that put in the claim stated that VW are knocking back so many claims right now, for spurious reasons.
It's been stated that Golfs and other VWs that have either been new models or facelifted with the Golf 7.5 or after now have detectability for boxes/remaps - prior to that time, they were thought to be undetectable.
VW engines and the fuel system are pretty robust (except that awful twin-charged 1.4), so you're most likely to hear from someone with a dud turbo that requires warranty work on the drivetrain. Doesn't happen often, but the actuator went on my R's turbo at 6 months old and the turbo was replaced. Similarly, I had a turbo fail on my 2003 Polo 1.9TDI in the same way at 5 months old - 11VAGs owned from new, 2 needed turbos under warranty.
As you may not get a definitive answer to whether VW can and do detect remaps and boxes, I'd have to assume that they can and decide if I want to risk binning my warranty should the worst happen.
You probably won't need major drivetrain work under warranty, so you're playing the odds if you remap.
If you have a manual box, be prepared to stump up for a new clutch either way and wait at least a yearas the drivetrain is more likely to fail in year 1 than years 2 and 3 due to incorrect assembly or defective parts as it's in heavy use from day 1.
My recent experiences with VW are that they are in serious penny pinching mode right now and will deny any claim they can - goodwill gestures from VW are no more.