At this stage nobody is faking any death. The reports are based on social media posts hinting at such. There's been no coordinated attempt to fake a death.
As for the passports unless you want to get from Syria to another country and that assumes the border is functioning, what's the point? They could go Baghdad or Ankara or Dubai and ask for a new passport assuming they don't have their existing passports.
You can't guarantee you know how she died at all. The reports suggest she died as a result of poor medical care after a fairly routine operation which is as equally plausible as the scenario you seem certain about.
I also don't want to live next door to a gaol. Should we not have them? Everyone wants great neighbours but there are laws too. Do I want them backin Australia? Well frankly no but they are citizens with rights, particularly the minors.
So your saying its not plausible that the couple would fake their own deaths, for their own different reasons? I'd beg to differ. it would be extremely advantageous to both of them to drop off the radar.
What's to stop her from taking on the identity of a local Syrian who has either fled the country or been killed? And then joining the waves of illegals flooding into Europe and the West seeking asylum? Or better yet, marrying a Australian under her new false identity and seeking direct access to Australia? All very do-able with the appropriate planning and connections.
As for the reason she may have died. The reports say she had an existing appendices issue before leaving Australia. Common sense says to get the matter operated on in Australia, as taxpayer's expense, and in modern and sanitary facilities, before fleeing to a third world hell hole with no capable medical infrastructure. If you are taking a calculated manoeuvre to flee the country, you would surely have enough brains to plan ahead and take care of existing, potentially deadly, medical problems beforehand.
As for the last comment about living next to a gaol (I hate that spelling by the way for some reason), well if you live next door to a jail its because you chose to buy a house next to a jail. Not so if your suddenly waking up one morning to find Mr Beheading's family has moved in (your also most likely a recipient of public housing, meaning your ability of packing up and moving to a different place are slim to none).
You trying to go off the 'facts', but the facts as we know them are mostly unknown and potentially orchestrated whispers coming from a land where there is no way to access reliable first hand information.