I used to be a fire warden at my place of employment. Only ever had one genuine incident (someone burned some toast and set the smoke detector off!). Two things used to amaze me when we had practice runs:
1) Most people would evacuate pretty quickly. They might collect a coat and/or mobile but the delay was minimal (yes, they shouldn't but I took the view that given the funnel effect of emergency exits and stairs an odd second here and there was not an issue in a practice). However, there was always someone who had to extracted, usually because they were incapable of terminating a phone call. On one occasion I took the phone from the hand, said "we have a fire alarm, he'll call you back" hung up and chased the offender out.
2) More relevant to your question was what happened outside. The idea was that you went to an assembly point, found your warden and "reported". Then, when the warden had accounted for everyone, he would report to the head warden. The idea was that we would then have an idea if anyone was stuck inside for the emergency services to rescue. This was where it really went wrong. People would continue meetings, get on the phone, sneak off for a smoke, go to their car and take an early lunch and the warden was left to search them out. Now, bear in mind these are people who've had a briefing about what to do (admitedly some time previously, not usually in the preceeding couple of hours as on a plane) and most of them had been through a practice at least once.
On a plane, the "what to do after you're out" instruction is usually a simple "and move away from the plane". No idea of how far (personally I'd get as far away as possible!), no idea of what to do once you are "away". (Would it do any good to say something in the briefing, probably not).
Ideally I reckon you send a couple of CC out first to organise people but, of course, in these days where there are often fewer CC than doors and the responsibility is to evecuate the plane that's not possible. One is therefore left with having to wait until the CC evacuate by which time the AFRS is likely to be pretty close and I can't help feeling that at that point responsibility should immediately pass to the AFRS. But then I'm not CC just lowly SLF.