And what if you kill his daugher? ^^
The quote doesn't tell us that, and I'd say it depends on how this works. If the daughter is actually an NPC the game randomly generates to replace the dead character who is then said to be his relative (Since the game has randomly generated quests, I could very well see it having randomly generated NPCs appear as well.) then it could potentially allow you to kill off the person infinitely and get infinite replacements (That sounds really weird when you put it like that.) or maybe if you kill her too, then the quest just gets broken, we'll see.
It must also be said that just because some quest givers are killable doesn't mean all of them are killable, maybe only characters involved with side quests are killable, or maybe it even only applies to said random quests. I could very easily see the game using essential NPCs like Oblivion for the main quest, we'll just have to wait and see. When you assume things that weren't explicitly stated, you run the risk of being proven wrong.
"Killable questgivers" is nice and good unless they get killed by random critters that chased the player into a town...
I agree fully there, if I kill an NPC and end up breaking a quest because of that, then it's my own fault for doing so. If I don't like it, I'll reload, or if I did not know about it until I had overwritten all saves from before that characters death or it was so long ago that I'm not willing to replay all that, I simply won't do that quest, or I'll start over with a new character, but when quests get broken due to things outside of my control, like NPCs getting killed by enemies when i could not have helped them, that gets annoying, choices and concequences are great, so long as the concequences are for choices you made. When you have to suffer the concequences for things outside of your control, it's just annoying. As long as Bethesda can find a way to keep quests from being broken by important quest givers dying when they decide to go for a walk out of town or during these dragon attacks the article talks about, though, I'm all for letting players kill any game character they please.