Oh right, I don't do anything to restore initial settings. Less of a concern on emulators. (And in EGA or VGA it's liable to remain stuck in faux CGA mode.) Should it try to set 80x25 on exit? Or is there a sensible way to detect and reset things?
I have been scrolling through esoteric documentation for days and the video setup is still 80% copy-paste and 10% guesswork. At least I got the snow to stop.