In my game for the Xbox, vampires wiped out most of Whiterun, sadly no NPC's respawn or take over jobs as needed. It had gotten so bad I decided to move to Riften, and now they are attacking Riften. I have found though, that the less you fast travel to your home city the less they attack that city as you will mostly be attacked while on the road or in the wild while you are out adventuring.
After a Master Vampire turned the Blacksmith Balimund into an Ash Pile in Riften , I began using the city stables as my destination for fast- travel . Now both Horse-Crusher and his assistant are gone as well.
The random encounters with marauding Vampires and the Travelers seem to be set up like the Dragon attacks. After a period of time without one (usually 48 hours) , an attack will be due somewhere.
Because Fast-travel speeds the clock up , attacks frequently occur just after arrival.
If there is a location that you are genuinely interested in protecting , I suggest NOT going there until just AFTER a Vampire attack somewhere else. This will hopefully provide a window of opportunity to peacefully conduct your buisness and get out before trouble starts.
If you must fast-travel to a larger city , go to a spot where lots of guards hang out rather than the buisness district(i.e. Blue Palace, Dragonreach, etc.) , then wait 1 hour. If Vamps are around they should attack you there and it`s less likely to result in NPC deaths. OR fast-travel to a nearly farm or the stables.
The Travelers are easy to spot in their Black Hooded Robes . They usually don`t attack immediately , but will walk a pre-determined route until you get close to them. You can sometimes entice the Traveler to follow you by approaching(not too close!) and backing away as they notice you. You can then lead them to a safer spot for your fight. Or you can sneak attack them when they`ve got to a spot you prefer.
Doing that 1 hour wait upon arrival helps save lives because the NPC will have had time to get from the location where they respawn into their place of buisness. This helps some with inside vendors like Belathor