After installing Dawnguard I have started losing NPCs in towns, especially in Riften (Madesi was killed by a vampire). At least Whiterun and Solitude are also places where vampires might attack during the night.

Any way to resurrect tose dead NPCs by console ?

I would not want to lose characters for nothing, especially vendors.

click on them, then type "resurrect" without quotes.

At least it worked in Morrowind and Oblivion.

Yep it works in skyrim too.

But what if the dead NPC has already rotten away ? Then there is nothing to click.

if there is no body, I suppose you can't resurrect them. There must be another command though, but I dunno

That's more invovled.

You'll need to find their formid in the CK, and then type something along the lines of "(formid) placeat.player"

coc WIDeadBodyCleanupCell, and find the stripped dead body of your friend.

Not recommended to resurrect NPCs, since there is no way to reset the dead count, which will screw up dialogue. Also, many townsfolk have scripts to whisk their body away and deposit their items in a burial urn in their city's Hall of the Dead, so you shouldn't resurrect until that happens.

Better to reload and use to console to make the person you don't want to die essential.