Electrical Ditch Cover Inspection
Conduit in place should be fine for the inspection.

The forces involved in pulling make doing so without the conduit buried (so it stays put) rather difficult, and in any case it's quite common (and it you have not, I suggest you go get some) to put empty conduits in a trench for future use (i.e. a small conduit for network/phone/communications.)

I have to assume that something makes it worth the extra run up to and down from the attic rather than simply entering the building on the level of the main panel.

I would NOT leave the wires exposed in the attic. I'm dubious that it's acceptable, as they are not cable, designed for exposed use, but in any case I would not do it. I've seen way too many chewed cables in attic spaces. Completing the run in conduit should not be terribly difficult, and gives the wires protection.