Bethesda, please, issue a fix for this. Preferably a "Revive NPCs" item or button that can be hit. If the PCs were replaced by other PCs populating the towns and shops, that'd be fine I suppose. Whatever. But they aren't, and this is mind bogglingly frustrating.
I don't know what meeting or team decided this would be cool. I know some players WANT to kill off their npcs, and hey, whatever floats their boat. But for the rest of us, loosing access to merchants/quest givers is really aggravating.