I think if you do a DIY booking the onus is on you to keep abreast of the current FCO advice while out there incase it changes, whereas a regular TO such as Thomas Cook, or Thomson are obligated to get you back, so I think they will send out extra planes in an emergency situation to fly people home, and they will have a communication system of some sort in place to inform their clients.

I have vague memory's of something like that happening in Tunisia a couple of years back when there was the Arab Spring and there were pictures on TV of folk scrambling to get back to the airport.

I think the other thing you need to do is make sure that your travel insurance is the correct kind for a DIY package, I'm not an expert but I think there are insurances that give extra cover but I guess the premium will be a bit more. It's possible that if FCO advice changes while you are out there you will have to pay for your own flight home and then claim it back via insurance so you would need the correct cover.

Although in fairness to easyjet they seem to have been very flexible with people who currently have flights booked to Sharm, and are letting them change destination even though there isn't a travel advisory against Sharm, which they aren't obliged to do.