This might not be entirely accurate, but it gives you a good idea. Here is the site stats for Derpibooru.
https://derpibooru.org/pages/stats
If you look, the uploads have been pretty consistent for a few years now, maybe even increasing a bit from Season 5 to Season 8.
I would say no, that fandom isn't dead imo.
btw, welcome!
Want me to be honest, I started watching right around the first Equestria Girls movie back in like 2013 between the season 3 and 4 hiatus. I thought that was late, but I guess not.