I suspect that, like Norway, the UK will commit to the next phase and book slots, paying penalties if it subsequently cancels.
It will do so without any guarantee as to exactly what the aircraft's capabilities and characteristics are, and with no firm guarantee as to what it will pay for the privilege. It will do so as part of a high risk, high cost programme that is almost certain to run into difficulties as a direct result of having to make production investment before enough of the development programme has been completed.
We should not sign up to JSF, if samity prevails, but I suspect that we will.
Without operational sovereignty, however, I'd hesitate in predicting that the F-35 will ever actually enter UK service.