At Brickfair 2019, one of the biggest things that surprised me was the number of Bionicle fans who got into it after it ended, or got into the original because of the reboot. But it makes sense, Bionicle is overall aimed at younger people, and a lot of them weren't around/old enough during the first run.
As for the question of the topic, I think right now the advent of things like Wall of History actually make it easier for people to get into the Bionicle story compared to say 2011 right after it ended, even if they don't become part of the "community" so to speak. It's not too rare for someone to mention Bionicle to me, not knowing that I'm a fan or what it's really all about, and I'll just drop them a link to that.
The sets on the other...The recent growth of the community combined with how long they've been out of print for seems to have driven up the prices greatly, at least that's what I've heard. I remember around the initial cancellation, vendors at cons were still selling Bionicle sets and parts for dirt cheap compared to other LEGO. So there is that barrier to entry. I think we may end up seeing more story-only fans, or possibly people like your upcoming child who inherit their collection from a relative who was a fan. Overall though, I think there are still enough people getting out there won't be a real crisis or shortage of parts for many years to come. And that's only if it never gets brought back as you state.