Do guards respawn like they do in Oblivion? I'm guessing NPCs don't respawn but I want to check that too just in case. Guards are fairly easy to kill making them an easy way of getting Dark souls so long as they do respawn.
Yes they do, if you look them up on UESP you can see if they respawn or not.
Generic NPCs will respawn some time after they die. These include generic guard NPCs and the following NPCs:
- Imperial Legion soldiers
- Stormcloak soldiers
- Vigilants of Stendarr
- Falmer Servants
Source: UESP article on Skyrim NPCs