I haven't read it thoroughly yet, but
this article suggest that VW will kill "most" (word in the first paragraph) of its diesels in the US. My guess is they'll keep diesel options for pricier models but not for the likes of the Golf and Jetta.
The generation 3 (which your 2015 Golf is) fix involves both software and hardware changes, to be performed in two steps. The software change might be made available before the end of the year, but the hardware change will have to wait at least a year, with 1/3 of your compensation (should you choose a fix) being held back until the hardware modification is performed. As I understand it, the software change will take care of the emissions issue; the hardware change is adding sensors to ensure that the DEF system is doing what it's supposed to do. Thus, the hardware change shouldn't affect performance or fuel economy; however....
Adding new hardware to a working car is unlikely to make it more reliable. (I can imagine exceptions, like new hardware that helps take the load off another component that's being stressed.) These new sensors will need to be physically added somewhere, which means they could work loose and need replacing. They might be defective or fail, resulting in either a failure to detect a problem or a false alarm, which would necessitate a service visit.
Furthermore, the software fix is likely to mean that the DEF system is going to be running more vigorously than it did before, which means more wear and tear.
Thus, although I can't speak to the fuel economy and performance issues, I'd be shocked if the fix had no effect on reliability -- it's almost certain to decline. The real question is how badly it will decline. We may never know the answer to that question, of course, because as individuals we only know what happens to our own cars, and we can't peer into an alternate universe in which this scandal never occurred. Even VW might not know the true effects, since they can't peer into that alternate universe, either. The change might cause one in ten thousand cars to need an extra repair over the vehicles' lifetimes; or the sensors could be shoddily designed and cause half the cars to require extra repairs within a year of installation.