So I was just clicking around and managed somehow to pull my arrow off screen and now cannot get it back. Is there a way to reset the arrow to the default position?

It gets stored in your SavedVariables.txt, which stores all icon positions of default blizzard frames AND some frames whose position isn't specifically stored externally.

I have no SavedVariables.txt. Did you mean some lua file under wtf\Accounts\account-name\SavedVariables? Or in wtf\Config.wtf? I don't see such a setting in the latter file and the Questie.lua file is quite large. I'm losing my minimap player arrow when I switch back and forth between Carbonite and Questie and a reloadui doesn't restore it, but a full restart of the game does.