As for 2 years... given LTG I'd probably stick with QF, though my question is, if one has LTG and doesn't manage to fly the 4 QF~ sectors, do you still remain Gold status for a membership year, or does LTG override the 4~? (I would suspect yes, but unsure). in that case, your need to continue QF sectors would be minimal though if going to retain/make WP, the 4~ could come into play (I am not yet LTG.. ask me in a week lol).
Lifetime you don't need the Qantas sectors, the card has no expiry, you do of course need them if you want to get to Platinum so it is shown on your account, though they do say you need to keep status, but LTG (or LTS) that doesn't apply.