I'm an idiot. I'm not looking for help because there's nothing to do (my phone isn't rooted so I can't recover them after emptying the recycle bin), I just want to vent.
Whatsapp users will know that since last June or so, our automatic backups are eating up a LOT of space on our Google accounts. My backup (without videos) was over 9 GB and as a result my Google account was more than 97% full, so I wanted to free up some space.
I don't have a real backup plan for my phone, I just hooked it up to my laptop via USB from time to time and copied whatever I wanted to keep, then deleted duplicates. First red flag.
So I did this time too. It was slow and frustrating because the copy process kept getting stuck. I had to manually copy each folder, check after a minute if it was working, cancel the copy, delete the empty folder it created and start it again. Never during this whole thing did I stop and wonder if there was a better way to do it, which of course there is, there have to be a million better ways. But I've always done it this way and nothing ever went wrong (as far as I know), so out of laziness I kept doing it with the slow and painful method. Second red flag.
Near the end I was so frustrated that I didn't check the folders. This was the final nail in the coffin of a terrible backup. The "Whatsapp Images" folder was completely empty but I didn't realize until earlier today, almost a week after I deleted the stuff from my phone. Of course it was too big for the recycle bin, so it went directly into the Abyss.
All the pictures I was sent in the last five years are gone for good.
I'd like to end this on a lighter note, maybe say that I learned something out of this experience, but I'm not sure I learned anything. I'll probably keep doing stuff the wrong way because I'm lazy.
So the moral of the story is probably this: don't be lazy, kids.