I think they'd struggle to regenerate enough to keep the GR4 going for 10+ years on top of its planned OSD. We don't have a FJ navigator training system anymore! We've cut the force down to 2 front line squadrons and an OCU. I imagine the OCU would struggle with suddenly getting enough refreshers to stand up another squadron, never mind re-training 100-odd engineers, and moving enough people around the force to keep dilution and experience at sensible levels.
The 5th Typhoon squadron is just a flight right now but is in the process of standing up. Maybe getting the chequebook out and paying for the proper integration of the GR4's weapon set into Typhoon, and admitting that the original plan for 7 sqns (maybe 6 as a compromise!) was a better idea would help us sustain "years" of bombing IS.