Unfortunately, with the explosive popularity of Youtube and its explosion of gaming enthusiast content, it does seem like GT's days were waning. YouTube started a true race to the bottom as the amount of money to be had from YT video views was pennies compared to what GT was making on its videos at its peak (considering all the ad deals and that they saw all that revenue instead of a tiny portion like when doing it off YouTube).
It should also be mentioned that GT had production values out the ass. All the sets, cameras, production, graphics, etc. etc. by far surpassed the production values of the vast, vast majority of the videos YouTube's gaming personalities. It was television-tier quality (hell, a lot of that content actually DID show up on TV. They'd broadcast their E3 shows without missing a beat). But at this point you were having TV-quality production in an era where most of gaming-related videos were streamers, Let's Play'ers, people just talking to their bedroom webcam vlogs, etc.
It's pretty sad. I doubt we'll ever see TV-quality gaming shows like we got from GT. That business model seems to have collapsed
I really hope Keighly can work with some portion of the staff in the future, even just for E3.
EDIT: If someone can GT-ify my avatar I'd love that as well