.......it is true. I spent 15 years out of the country. I had to do tax returns for previous years when I returned, not all of them but quite a few. One would have to give up Australian citizenship or die before losing tax residency. Even death may result in tax obligations being passed onto family.
Roadblocks are generally checking road tax is paid. I have never been asked for a IDP, in fact I rarely get asked for anything. Just a courteous nod and waved on.
You don't lose your tax residency status unless you tell the taxation dept you are leaving permanently and settle all your taxation obligations. I left Oz for 15 years but had to catch up with several years tax returns when I went back.
.......Nah.....Cambodia is ok. There are far worse places to be. Australia is one. I spent a long time in Cambodia. Quite happy in Thailand these days. Kampot or Phnom Penh would be my choice if I had to go back, or even Koh Kong.