As far as I can tell, I seem to have recovered nearly everything, aside from possibly an odd bookmark or two. And, with all of my files backed up to the external backup device, later today I can set a new clone going, cloning the now-primary drive onto the non-booting drive and trying to boot from the clone -- this last to see if the drive is still physically sound.
While this is time-consuming and inconvenient, it's nowhere near as much trouble as it would have been to try and rebuild the computer from scratch. All of my applications are still running without having to reinstall them. That money I spent on a spare hard drive and a DriveClone license is well spent.
And because I once again have a computer that runs VPN -- it wasn't installed on the secondary laptop, whose primary purpose is to serve as the conduit for downloading sports and sometimes providing sound effects for Match Game SF -- I can again get to my company's network and can continue to work from home today, instead of having to make the trip today. That's a welcome relief on this first day back from "vacation."