Ugh, I hate questions phrased like this... no offense, of course, but it just irks me that people seem to either think a game is all anyone talks about, or it's dead. And it often feels like such a pointed question- either you agree, or you're in denial. At least, that's my personal experience anyway. I'm not trying to accuse anyone of doing that here.
Anyway, ACNH isn't as popular as it was when it first came out, but that's normal. That happens to most games. Add to that the fact that the completely unprecedented state of the world during it's initial release made it significantly more popular than ANYONE expected. It still has a pretty sizable fan community, and I see it continuing to have one for awhile. Add to that the fact that Nintendo is (slowly) releasing updates, it has the potential to get more popular again in the future.
From my experience, games like this (with a lot of content, and more content added regularly/semi-regularly) tend to have ebbs and flows in popularity. There isn't so much a "dying" (which, again, feels like SUCH a loaded term) as a natural interest that wanes. If/when Nintendo releases big updates- the farming that's been rumored, more NPCs, The Roost, more holidays/events, etc.- people are going to see that and say "huh, I haven't played in awhile... maybe I'll see if the update's any good" or "I didn't want the game before, but dang, that looks cool... maybe I should give it a shot now" and it'll pick up in popularity again. Then people will play the heck out of all the new content and move on to other games. And then the cycle continues.
And here's the thing with ACNH- early on, Nintendo confirmed AT LEAST two years worth of updates were planned. This game has been a huge moneymaker for them. Even the most cynical of players can see that it's a huge deal. I have a feeling we'll all be saying "For Nook's sake, it's been ____ years, LET IT DIE ALREADY, NINTENDO" before we're lamenting that this game died too soon. If anything, I imagine Nintendo will be releasing new updates (and, if I had to guess, at least some paid DLC) for a long time to milk every last cent out of this game. I mean, just look at ACNL- how long was it between games? They revived that old game, which was already pretty great, with an update years into it before they made a new one. I can't imagine ACNH is going to be any different.