I was going to slip a quick quest in while up in Windhelm, i.e. the one about dock workers wages, but I've searched the docks from one end to the other, checked in the warehouse, waited around and searched and checked again. Has he gone marsh-scouting, or might he be dead from some vampiric, bandit or dragon mishap?

Did you check inside the argonian quarters? That means, the great room at the dock, where all the argonians do sleep together?

It was daytime, but I'll go look...

Checked the whole darn city then snuck into the Argonian Quarters and found him asleep there - idle sod. As it was not a good idea to sneak into the Argonian Quarters, I will have to sit outside in the cold with the fish and dead bodies until morning. So much for a quick quest...

EDIT: I should point out that the door was permanently locked, so I had to break in at night, and was arrested as soon as one of the Argonians spotted me

Nope. Waited all night and most of the morning. He never showed up. Am I looking in the wrong place? Is there another bit of the docks? Or does the green scoundrel disappear on week-long benders which he then sleeps off for a week?

He might've misplaced his key and locked himself into the Argonian Assembly quarters. Best time to check the quarters without lockpicking is between 6am-8am or 6pm-8pm