Warning! Warning! YesTAM has had experience of this type of arrangement that is in effect an invitation to resign. The letter may talk of "leave without pay", "furlough" and all sorts of other stuff, including promises, incentives and all sorts of honeyed words. However in my case (I think the letter was drafted by Oldmeadow in person), there was this little clause that says "For the purposes of company records, you will be shown to have resigned". In other words, if I had accepted the agreement, no mattter what honeyed words it contained, and wished to return a few years later, I was ****ed.
If you really wish to enter an agreement to do this, it must state exactly how you will return to Qantas, in detail. Furthermore, it must also spell out the consequences of what will happen if you or Qantas fail to exercise your rights. Watch for the clause at the end (or the beginning) that can be construed to destroy all the other clauses. If you do not understand it, get advice.
To put it another way, it is no good saying for example;"After thirty days this option will lapse". You have to spell out exactly what your rights will (or won't) be after the option lapses. Do not leave anything open to interpetation because anything left hanging will be used against your interests.
Words that should ring alarm bells include: "At the company's unfettered discretion" (Meaning they don't have to be "reasonable") and anything that gives the company an option to terminate your services or not offer you a position back.