Try saying his name three times into a mirror with the lights turned out.

Bloody Mary. Bloody Mary. Bloody Ahhhhhh

If he isn't back within the next 8 hours we should assume the worst.

Likely causes:

mauled by kangaroo.

Went to water his garden and accidentally picked up a Taipan mistaken for hose.

Loss of internet.

Was showing off all the latest surf stunts and eaten by great white.

Funnel web spider in boot.

Skydiving accident.

Maybe he went on walk about and the dingo's ate him :]
Got married to a Roo named Matilda and hopped away happily ever after...I hope he closed the gate. :]

#5 hope it's true. @ bunyip deserves a happily ever after.

All your possibles are more valid than maybe you thought except for sky-diving accident. Only way that could ever happen is if one of them fell on me while I was doing any of the other ones :)

XD Or a volcano eruption happened and at the same time, a tsunami, meteors falling from the sky, earthquakes... lol