Thinking that Dani had fallen asleep was a logical assumption only because it could happen to
anybody. There's no reason to think that Dani had ever done that. A pessimistic person might have worried about a car accident, but no one would think, "My best friend didn't show up for dinner, therefore she must have been abducted, raped, and murdered."
In this news article, Dani's father stated that abduction was the "only plausible explanation."
http://m.huffpost.com/us/entry/us_58502bc9e4b04c8e2bb207d1
LE has made it clear that they share that view.
It is reasonable to conclude, then, that Danielle's abduction was the reason why she missed dinner. The idea that she blew off her dinner plans, which would have been completely out of character, but then happened to be abducted later strains the credulity of even the most gullible. It is clear, then, that she was abducted
very soon after leaving Met Life, before she was late enough for dinner to warrant a phone call.
Few people (or few people without ulterior motives, let's say) would still argue against Danielle's having been at the security guard's house soon after she left work. That places her with the security guard, who "has nothing to say to the police,"
at the time of her abduction.
There are many possible scenarios and a few plausible scenarios (all involving the security guard), but only one
probable scenario.