The .40 s&w fallout is sort of a shame, but Ive never owned personally a .40 s&w. It is close enough to .45 ACP and 9mm (40 technically has more power than both) but for better or for worse, its in the same ballpark. I know all about the .40 s&w capabilities and have fired thousands of .40s&w through the years. I've always liked it, however Advancements in research and technology have now shifted back in favor to the smaller 9mm.... however I knew it all along, that 9mm was just fine, even with the older jacketed bullet technology such as HI-Shok, Hydra-Shok, and non bonded Golden Sabres (which all 3 of these are still in my magazines, and are for my purposes just as good as any bullet out there)
The fact that thousands of these older jhp bullets designs have been cycled through my 9mm carry guns without failure is more valuable to me than some new chomed out designer "botique" bonded XTS-DSPN-JHP +P with elastomer filling so the cavity doesn't plug.....one which is $1.50 per round and you can't afford to fire more than 20 rounds of it in testing or you'd be broke.
About 20 years ago I was purchasing my first "defense style" handgun. This was at the peak of the popularity of the .40 S&W, and at this time i believe 100% of LE that I knew of used. 40. I knew the FBI used 40. And I had my eyes on a Glock 23 or Glock 22.... so was at a local gun show, back when gun shows used to be good, and had made some sort of deal just about every show I attended.
A reputable FFL who's prices were as fair as can be, and who ive bought from before, had a number of Glocks for sale, and I was looking at the G23 and G22...... the guy asked "Why" the G23 or 22, and why not the G17 or G19?..... he then went on to explain that the 9mm was cheaper to shoot, higher capacity, less recoil, easier to shoot.....and other comments as well. He convinced me of getting into the 9mm based on my needs.....and low and behold I left with the G17. I thank Mr. -----? who ive never seen again, for showing me the way back then, and talking me out of the .40 and to use logic rather than just use what the Govt. uses just bee-cause.
I think the .40 s&w is just a fine round, and I don't think it's going anywhere anytime soon. It's popularity is however decreasing. In the hands of a steady handed, well trained professional, the .40 S&W has an edge over 9mm, and always will.... But, there are needs out there to fulfill that are not about the caliber and performance of the round itself; a round which is and always has been a great one. The 40 Smith and Wesson.