@carlosjeurissen: Thanks for responding

Does this recent update mean that THIS "Shortcuts for Google" is going to be deprecated in favour of the other one, "G App Launcher (Shortcuts for Google)"?
They seem to be exactly the same now, except of course for the override options of the latter and the information in this one, that it's been replaced.

BUT.. even if you're planning on taking this extension offline at some point, keep it online for a while, so that most users will likely have updated this and seen the message.
Or you could try to get Opera to merge the two extensions, if that's even a thing.

I appreciate the hints/ideas.. Though there's no automatic File History for those user-specific directories and I only manually create System Restoration points for the more significant Windows upgrades/service packs or hardware changes.

It seems that Recuva could restore some of those files that were simply deleted (like the Extensions' directories), but none of the files Opera simply overwrote after resetting all settings.

Apparently I'd have to have a program that actually quarantines those files or at laest logs file changes (like the NILFS file system, or Windows' File History which I never needed before, and also causes System Volume Information to become uncontrollably huge).

There's a "backup" to my Opera files that's a few months old. I honestly won't bother with it though, since it's too old really and too much has changed, so I'm better off with this new profile (except for the synced bookmarks of course).

OK, this is more of an FYI kinda-bug-report to the people possibly involved with forwarding these things to the devs or QA or whoever, though if anyone cared to actually explain some of this, that would be nice too.

So, yesterday my Opera was working fine, and then it updated itself and I usually just take note that it does that and don't think much of it. I'm assuming that it updated to the next major release version (45), at least the about frame now says this:
"Version: 45.0.2552.898 (PGO) - Opera is up to date"

Couple hours later, I again start up Opera and at first it looked like it was opening the original window and then closing it right after, and instead it created a new window that looked mostly(!) like the one it creates after a clean installation. But then it put up an error message telling me that some file was corrupted or something and it apparently that meant it couldn't load my profile at all.
Instead of closing down immediately, though, and subsequently giving me a chance to take a look at the problematic file(s) first or at least backup my damn profile, it just overwrote(!) my profile with its default settings! (including the bookmarks file, without creating a backup in the process!)
It even cleared the "Extensions" directory without ANY kind of notification about its actions.

So, yea, what the hell, something obviously went horribly wrong after that update.
This system is otherwise clean & healthy according to the best of my abilities.