Mr Boffin,
While there is no formal Plan B, everyone is being forced to make their own Plan B by the fact that what was originally a 2010s aircraft is now a 2020s capability.
The RAAF has bought SH and may buy more, the USN has bought SH (although unlike the DDG-51 restart, the SH cost is predictable) and the USAF is into major SLEPs.
Operationally, mixed stealth and conventional fleets will be the reality throughout the 2020s. For most of the world, this means evolved-Teens and '35s vs. Su-35/T-50 and J-10B/J-20. Oh my...
And even the above applies only if LiLo or Charlie is really, truly serious about rehab this time, and for once in its lifetime the JSF program stays on its planned schedule and cost for more than 12 months, and if the hook issue is soluble within weight and LO constraints, and if the operating costs can be held to a point where the customers don't start to choke....
It's time to start thinking about what decisions should be made in one or two years' time if the prognosis gets worse. That does not necessarily mean changing JSF plans, immediately, beyond what has been done.
GloJo: The reason that the Marines went for supersonic is that (from day 1 of the definition of a Harrier follow-on, and in parallel with the UK) they wanted a competitive air-to-air fighter with sustained 9g (whoops) and that if you design one of those, M=1.5 pretty much falls out. The reason they went for stealth was that they were promised that it would not cost them anything, either in performance, money, schedule or risk.