In the video from SkyNews that JamesKing posted a few pages back, Darroch said that Corrie was in good spirits during the phone call and Corrie was looking forward to his night out.
I got the impression that when Darroch answered the question about how Corrie normally got home from a night out that Darroch was saying that if the group had all decided to get a taxi back, then they'd get a taxi back, and if they hadn't made group arrangements then Corrie was capable of figuring out his own way back.
In CCTV1, Corrie looks pretty nonchalant to me. He doesn't look as if he has anger or sadness building inside him, he just looks like he's confidently (albeit a bit drunkenly) focused on finding a place to sit to eat his food.
How big is the Flex club? Could someone go off to the toilets or to the bar and be far enough away from their mates (who are probably talking to each other and a few girls and not looking around them) to leave without anyone noticing? Is there some reason his mates wouldn't just think he'd got off with a girl?
Also, I was thinking back to the thing about Darroch being the one to get the message that Corrie was missing...could that have been a message on the home phone that he picked up while Nicola was at work? Could it have been a Facebook message...maybe he's FB friends with a couple of lads at the base, or he was just the first family member to pick up the FB private message, which Nicola didn't check first due to her being at work?