Yesterday, I was wandering near Ivarstread, when a Dragon shows up. I ran to the village to get some help from the guards, and the innkeeper, Wilheml I think he was, came out of his inn with his wife to fight the dragon, but it kill them. Today I went there again, and they still dead, does it means Ivarstread will be without inn forever??

You can check http://www.uesp.net/wiki/Skyrim:Skyrim to see if an NPC will respawn or not.

Also, if you are using PC, you can try the resurrect command

Don't believe they will respawn.

seems like this never makes it in a game i know killing someone and them coming back, for some may break immersion and all........ but come on shop keepers at least should come back

EDIT: or at least a nameless npc should take their place after a while.

I checked out that wiki, and it says Wilheml is "essential", and essential character are not supposed to die! D=
Anyways, I will look for that resurrection command and try it.

Thanks for the answers.