I don't feel comfortable saving anymore out of fear that NPC's are being killed every time I stay in a town of an extended period of time. Takes the fun out of the game having to worry about things like this. The odd dragon killing a quest giver was bad enough.
The random vampire attacks and the mysterious traveler have to be the worst additions to the game and my only real complaint.
Kill Harkon and the Travelers/Random attacks will stop.
Right after downloading Dawnguard , I had a bug that blocked the DLC main quest at Chasing Echoes but I kept playing for a while anyway.
Many, many NPC deaths occured during this period due to the vampires.
When I finally had to load a pre-Dawnguard save in order to break the blocked quest , I tried to go straight through to the finale with Harkon.
By avoiding other quests and not making many side trips during this , only a couple of guards and ONE named NPC died in attacks. In my case , Pantea Ateia was decapped by a Master Vampire in Solitude when I stopped there to unload some Heavy Falmer armor.
With the pressure off , I was able to return to the Dawnguard radiant and side quests with more peace of mind.