It's cyclical in a lot of ways. I've been going through some of the earliest back-issues of OGR (OSR, then) from the 1970's in the Digital Library. There was no Internet for forums back then, but there were letters sent in to be published. Often with the same concerns -- Is the hobby dying out as participants age/where will new participants come from?... Scale vs Tinplate... 2-rail DC vs 3-rail AC... Is Hi-Rail scale(ish) or still tinplate?... Why must O always be second-fiddle to HO and N scales?... Are prices for O going out of reach?... The hobby is dying because company X is closing shop... The hobby is growing because company Y is now making O products... The hobby is saved because company Z is now making company X's old product line(s)... What we would call "flame wars" in forums today played out then in slow motion, time-delay, imposed by the postal service and publishing schedules.
And the advertisers included tell the story of ups and downs in the hobby as well. The magazine started when O was probably on an upswing compared to prior years at least in the realm of kits and imported brass, while Lionel was in the difficult transition from bankruptcy into rebirth under MPC/Fundimensions. Williams hadn't quite entered the market. Weaver was still just Quality Craft Models and in startup mode. Atlas was just adding O scale. Walthers was proudly announcing how much they were growing. There were other manufacturers who would later disappear or get absorbed by other names, in whole or in part. Remember All-Nation and others?
Interestingly enough, if there's ever been one constant in the O gauge world, it's Lionel. Virtually everything else has come and gone, both in the scale and tinplate world. Yet some incarnation of the Lionel name has been at the center of it all. The company changes, but the name remains, and the products are sometimes proudly kitbashed into new things or cannibalized for their whistles by scale enthusiasts even as they complain about Lionel "toys" not being good enough.
When I came into the hobby in the late 70s, kits were starting to fade in favor of ready-to-run, and that cycle really seems to have reached its peak with so many RTR manufacturers and MTH's parity with Lionel. MTH's exit may leave a hole in the RTR market -- but is it time, maybe, for a resurgence of kitbuilding and craft work? Today we have technology like 3D printing and laser cutting -- technologies that can enable the smaller "cottage industry" producers once again. We take color inkjet and laser printers for granted; those technologies can print on media beyond just paper. (Although for decals, we STILL need a cost-effective technology to print white!)
So maybe we've hit another major change/turning point in the hobby. Instead of worrying, maybe it's time to look at what's out there and what new or revived directions the hobby can take. Time to be excited, not fearful.