OK, here's how this breaks down...
I'm now on my second playthrough (as a VERY new player to the Fallout games) because I couldn't complete a certain quest for which I needed my dog as a companion. Why, you ask? Because I think I actually deleted him somehow.
I was using the Workshop function to scrap all the unsightly junk in Sanctuary one day, and getting carried away. I came upon several doghouses during this time, and scrapped all but one. I haven't seen Dogmeat since.
He was not my companion at the time. When I started looking for him, I couldn't find him. Went to Red Rocket; no sign of him. Started visiting all the settlements I'd been to. No trace of the mutt ANYWHERE.
Then I read online that he will usually be found in a doghouse, waiting for you. And that it could be any one of the 5 that are found in Sanctuary.
Uh-oh. IN a doghouse.
As I reconstruct events, I think I came up to a doghouse from behind, and scrapped it- not realizing that my dog was actually lying down INSIDE IT at the time. I know for a fact that when you scrap a container (suitcase, shelf, even a safe) it deletes whatever is inside; so scrapping the doghouse.... deleted Dogmeat. Poor little fella.
I've been told this is impossible, but I can't think of any other answer. I'm already deep into a second (and better, now that I know what I'm doing) game, so it's really academic in any case. But I can't help wondering... has anyone else heard of (or actually done) this?