Andro - that's exactly what I chose to do. I went back to an earlier save from before joining the Dawnguard. Thankfully, both Lod and Kust are still alive. When I reloaded the vampire attack never happened. Of course they could always get killed later on ...

I have character commitment issues. After having been playing Skyrim with all DLCs on x360 for a couple of years I have a habit of getting a character to around level 30 or so at the most and then rolling up a new character to try a different play styl...