i know that lod can die before he triggers the A Daedra's Best Friend. and after 15 hours of game play, it seems that silus vesuius, a quest giver, has died in a dragon attack. so i have to restart the game.

any other named quest givers that i should get to before they can die?

I think it's just better looking it up at the uesp. There are so many quest givers that it would be difficult to give a list.

You will find it considerably easier to rule out who can and cannot be killed by viewing this http://www.uesp.net/wiki/Skyrim:Essential_NPCs. On an additional note, the likelihood of you having a flawless playthrough borders on the realm of nonexistence. I may recommend you temper your proceedings with priority in mind -- what quests you'd like to accomplish, what artifacts you'd like to possess, etc. and how some of your other actions may have a direct or indirect impact on those quests.

^^^^ second those. Plus you yourself can kill someone that will cause you not to be able to do a quest. Not alot of choices in the game, but their are a few. ( not that you know it)

well that page is going to help

found out that silus vesuius won't appear until level 20. not level 20 yet, so i don't have to start over.