Based on how far the F-35 project has gone now I get the impression that, at least for the conventional take-off/landing variety, "falling over" entirely is pretty much impossible (especially once you consider who is relying on it succeeding). I'm sure there's a chance that some capabilities might not be quite what some were hoping for (as in all large projects).If for any reason the F35 should fall over, taking too long to be available for instance, do we have a plan "B" ?
Additionally, if the F-35 were to "fall over" then it wouldn't just be Australia looking for a solution.
I think it's safe to say that the F-35 is a fairly safe bet now. I'm not sure what projected production time frames are looking like these days, but I think an interim solution is probably all that's needed if things don't go as well as hoped (i.e. maybe more SH if required, and reducing airframe flight time of the classics where possible).