No one seems to know if NPCs ever respawn or not, so I'm not even going to ask. I did a search, and it seems as though everyone's just guessing. If you do know something definite, though, I'd surely love to hear it.

But has anyone actually seen a slain shopkeeper replaced by one of their relatives? Given that dragons appear and roast villages and such at random, is there some kind of a mechanic in place to prevent Skyrim from becoming totally depopulated?

I haven't seen anything respawn. The deer I killed outside Riverwood is still there after 50 hours and several in-game weeks.

Yes, I have seen it. Riverwood has a good example.

Everything outside respawns in 10 days. Dungeons a month. In-game of course.

But "townsperson" NPCs don't respawn at all, unless there's a relative handy to replace them?

This just seems odd to me, as one of the touted strengths of Skyrim this time around is "infinite content" — but shopkeepers are an important part of that. I'm fairly sure I've already lost a traveling Khajiit merchant to a waterfall.

Ah well.

I will be pretty disappointed if shopkeepers don't respawn. This would turn the awesome fact that dragons can attack towns into a horrible mess. There are enough generic shopkeeper lines that I don't see why it couldn't happen.

Talking of shopkeepers, i SWEAR TO GOD/TALOS/DIVINES/ALDUIN that i heard the riverwood traders voice on some other dude in the game... 100% sure!

I killed the dude at the Tavern in Winterhold and his wife took over.

If they have no relatives they should have it so you can buy the building and make money from it.