Trust me, It will be after a month of inside game time.

Sounds fun
I do most of my transactions with thieves guild fences so it doesn't bother me lol

Its only the beginning from what I read. More attacks will happen in the thread starters game which will result in more erased NPCs the more him or her plays. Eventually this awesome game world will be reduced to guards and essential NPCs making the game world pretty much lifeless.

I hate traveling to Riften and having Dawnguard attacking. I have 3 people dead already 'cause of them

It happened to me twice so far (level 18), both times in Whiterun. First time didn't even see what happened - only saw Carlota Valencia's ash pile and the dead bodies of a Master Vampire and his two minions. Second time I was ready and killed the [censored] with Dawnbreaker. It could get annoying over time. If I lost a good NPC (like the blacksmiths, main merchants, etc.) I'd reload for sure. Didn't really care about Carlotta so I left her dead. The ash pile is still there though...

It's the only thing I'm not sure about so far in the DLC.

Yeah, there's a mod for PC that makes civilians run indoors when a Dragon attacks, leaving only you and the guards to deal with it. I think there's probably gonna be a mod like this for Dawnguard too on PC when it comes out. But yeah, on consoles, it's pretty [censored] up.