QF or AA could drop their club partnership agreement at any time, in which case your QF membership would no longer be valid at the ACs. I had previously thought this made the QF lifetime membership a bad deal, but the more I think about it, the more it seems that the QF lifetime membership could be a good deal. As others have pointed out, QF is likely to survive at least as long as AA. Also, I noticed that the QF membership gives you access to the BA lounges (when you are traveling on BA), not just the AA and QF lounges. So, you get into a lot more clubs with the QF membership than the AA membership. (It also gives you access to the US lounges when you are traveling on US, though those are small in number and decreasing in number.) Finally, if QF and AA did end their lounge agreement, QF would almost certainly pick up another partner, so if you're willing to switch your travel allegiance away from AA, you're OK.

Considering that the QF lifetime membership costs about half what the AA membership costs, and that there's no reason to believe the AA-QF club agreement will end any time soon, the QF lifetime membership does seem very attractive, especially in comparison to the AC lifetime membership. For someone with no status or Gold status, it's almost a no-brainer.