All previous saves are corrupt, we’re stuck in this timeline, I’m afraid.

It’s Fallout 3, just take (or cheat add in) the Puppies! perk. Spawns a new Dogmeat at Vault 101 if the original dies.

Of course, Dogmeat basically can’t die if Broken Steel is installed, and IIRC Broken Steel added that perk (IIRC you need to be level 22 or 24 to unlock it). Broken Steel made the non-human followers have nearly infinite HP. Fan patches may fix this, but on Xbox and PlayStation, you’re stuck with invincible Dogmeat — don’t aggo him.

Alternatively, speed run the main quest and start over. I think Fallout 3 can be beaten by a regular player who can’t exploit glitches and is moderately familiar with the game in like 2-3 hours? Once you get out of Vault 101, you just go to that one garage (I forget the name, but it’s easily found), do the simulation crap, then you’re basically at the final act. Go you know where, get captured by you know who, free you know who else, and then activate the you know what. Or rather, command you know who to do it for you.

Reload a save? We all know this game engine is outdated.