Will fading nostalgia eventually kill off retro gaming?
Its hard to dispute that retro gaming is hugely popular. The game collecting market has exploded over the past decade, sending prices of games skyrocketing. Systems like the NES Classic and Atari Flashback are selling extremely well. Games with an 8 or 16-bit aesthetic are popular, with titles like Shovel Knight and The Binding of Issac finding big audiences.
How much of the retro gaming boom is due entirely to nostalgia, with disposable-income-having adults seeking out games they enjoyed or never had a chance to play as kids? Once this generation tires of revisiting their childhood, will the retro gaming boom fade away?
Yes, retro gaming will die
As we've seen with the Atari market, the passion for the games of that era started to peak as the adults who grew up playing those games bought back into them, had a fun nostalgia trip and eventually got bored with it. Lets be honest, the games prior to the NES don't hold up that well, for the most part.
As we get older our priorities change and what was a fun hobby as a single person or childless married person, starting a family or finding new interests can turn your love of retro gaming into a pile of cartridges that you haven't touched in 5 years. We've seen this with the Atari generation and its likely going to strike the Nintendo/Sega generation in the coming years. The price of Atari games has been steady for the past few years and NES/SNES/N64 games rose in value consistently from 2012-2016 but seem to have peaked about a year ago. Nintendo 64 prices have already started to come back down.
No, retro is here to stay
Lets think about this: do people who were born after Star Wars was in theaters or the Beatles were a phenomenon enjoy Star Wars movies and Beatles albums? Of course they do. While it may not be a great comparison since the technology behind gaming is more integral to the experience than the special effects of Star Wars or the production values of 60's studio records, but what's important is how relevant the media of each is. Is Star Wars still an enjoyable movie? Are Beatles albums still great? Are Super Mario Bros. and Sonic the Hedgehog still fun?
I'd say yes, they are still largely as fun today as they were 30 years ago. While the nostalgia factor will wane with collectors and most younger gamers will turn up their nose at archaic pixelized graphics, there will always be people who are interested. People are still buying LPs in 2017. There's still a market for this stuff and it will continue as long as people have diverse interests.
Conclusion
Each console generation will see interest in itself reignited as those who grew up with those games become adults wishing to recapture that part of their youth and just as there are teenagers who've discovered artists like Green Day, Led Zeppelin and Stevie Wonder who were popular before they were born, there will be those who hunt down fun video games that predate them.
Retro gaming may shrink as flashy 4K 60fps HDR gaming becomes the norm and 8-bit sprites look primitive by comparison, but it will never disappear, it will simply evolve to cater to a niche market.

I agree completely. Plus the definition of 'retro' is always shifting. Games like Goldeneye and Mario 64 are regarded as retro today.
However I do feel that the first 3D games don't hold up as good as the old sprite based games, and thus aren't as 'timeless".
'Retro' will always keep expanding as new systems come and current ones are replaced. I personally classify anything older than last-gen to be retro, which would make Wii, PS2 and XBox retro in my book.
I agree about the first wave of 3D games. They simply have not aged well at all. PS1 and N64 games are either fuzzy (PS1) or muddy (N64) and while many of them play well, they're pretty ugly. Unsurprisingly, the games from the era that hold up the best are the 2D games released on those platforms, like Castlevania Symphony of the Night. Compare Mortal Kombat Trilogy on the N64 to Mortal Kombat 4 to see how much better the sprites look compared to early 3D graphics.
Oh man. You just gave me a sweet nostalgia flashback with mentioning Castlevania Symphony of the Night. What a game, what a game...
Its one of my favorite games of all time. Its just about perfect.