Hey that sounds like a good trip 2+ years, holidaying or working?
With regards to rolling over home data, it's certainly something worth considering, I say that as a customers, but certainly not something I've heard any whispers about in Telstra's back room, so to speak.
What you can do though, is three times a year Telstra will give you a data boost to get you back up to full speed for the rest of the month. More information can be found here: What to do when you've exceeded your Fixed Broadband Data limit
Enjoy your time returning to Australia.
