Summon commands can be used, this is the command
Summon DungeonBossRat_C
Once you have defeated him and he has given you the key, go to floor 5 of sewer, there will be the kidnapped npc
Not exactly sure how/where to input that command, since the only thing I found was the "debug" option in the keybinds section of the settings, and pressing that didn't appear to do anything. Also, updates for other things I found: the ruins(?) dungeon does in fact give you the emergency exit item even though the physical ladder is gone, so that's good. Tried out the cave dungeon and found that you can only leave every four floors, and that it does not give you the emergency exit items, but I swear I remember it being addressed in the next update's changelog somewhere, can't find where though. Though I did find another issue that seemed to only pop up in that cave, that being that while using passive combat, attempting to attack more than once in a row too quickly would cause the animation to either not play, or stop after playing, effectively locking the encounter and forcing you to quit/flee, though often it wouldn't even let me quit. Seemed to pop up most often when repeatedly using the fryup action from the skillet. Lastly, I've not tested it much, but after using two rock meat and one thing of fries while in the cave, I was able to take partial growth bonuses accumulated in combat, i.e. from the fryup action, out of combat and into other fights with a massive headstart. No idea if it's something to do with the food system as a whole, that cave in particular, those items, or what, but that's what happened.
It worked, and I thank ye, but now that brings up one last glitch(?) and I don't even know where to start with this one. Post-giant rat, opened the door in the sewers, and it's the real town smith in there. Cool and dandy. However, for some reason I managed to get him into town and selling me stuff before I did what I assume was supposed to be the introductory step of his quest, by finding the smith's key, later beating up the false smith, and then just talking to the real smith repeatedly after hopping into a dungeon or something to make time pass. I can only assume that I performed some sort of jank sequence break with all of that? Oh, and as an aside, I figured out what was up with the whole "knocking people down and having them continuously fail to stand up for the rest of the fight" thing: inflicting the stunned effect from weapons like the skillet says that it prevents movement, and in passive combat, status effects seem to be pretty much permanent within the combat instance, and the stand up action likely counts as "movement", so the action gets attempted and immediately fails without clearing the condition. So only maybe a glitch on that one, though probably still something that should be addressed, since stun+knockdown can win literally any fight right now if you're playing on passive, thus making the skillet+piledriver combo somewhat game-breaking.