Your fears won't happen if Apple follows the same method they've used since halfway through the 4 launch and the iPhone 4S launch. What the ARS staff will do is around 6 or 7 am walk the line and ask everyone what they want. They will give you up to 2 (two) iPhone tickets per person, you tell them what colour, size, and model, and they will ensure that they are in stock for you and give you a ticket listing exactly which phone you requested. You cannot change your mind once you get your ticket(s). The Apple Store only has as many tickets as they have phones in stock + some for contingencies. Ergo, by 8am you will know whether or not there is a phone(s) available for you.
My key issue is that unlocked phones should be available in store, as on the iPhone 5 launch they were online only.