There is nothing to fix, they will not do anything about it. They already gave the player plenty of options to get through a DLC challenge you chose to play, if your current character is not up to the challenge, it is up to you to adjust how you play to get the results you want. For keeping NPC's alive you would either replay your failures, till you got it right. or by avoiding the attacks completely and not going to any towns while doing the main Dawnguard questline. Or you can just uninstall the DLC if you do not want to play it. The developer having already given a way to avoid the town attacks, is not going to pay extra money to patch the DLC just to make it even easier.
So the answer is -
* Keep reloading and reloading
* Stay away from towns - keep away from large chunks of the gameworld while you rush through an add-on questline you may not wish to be doing right now and hope you're not going to get that bug where they carry on anyway.
* Uninstall the game you spent $20 on.
What an amazing feature. I can see how it really enhances the game. It's great they gave the player so many options.
I don't get why there's this persistent idea it makes the game harder. People report widely varying levels of attacks - adding a randomised NPC slaying mechanic does not make the game 'harder' - it makes it potentially irritating, contingent on how many attacks you personally get lumbered with. Some people seem to get hardly any, other people all the time.
Nobody argues random dragon attacks make the game 'harder', they just complain they get repetitive if there's too many. They could make another DLC where 20 draugr spawn inside Whiterun every time you enter it - that wouldn't make it 'harder', it would make it a pain in the butt to play.