I considered using the replacement tool to make a new train while transferring the cargo, but I didn't want to make more wagons (costs parts).
So instead, I scrapped the train and made a new identical one using the stored wagons. I didn't observe the train leaving the station, but the first time I checked the station after the train has left, the Crude is gone (screenshot is what Depot's dialog box looks like).
Did the train pick up the cargo because it knew it was assigned to a Network that could get rid of it?

I don't think I let the game run for long enough for my trucks to empty 2k Crude, and I can't find the Crude anywhere else.