a. Whatever, it will take 3-5 years to re-establish an operational capability from the go date.
b. The window for an RAF only solution closes when the seedcorners leave the building. After that, the RN will have to be part of the crew, because the RAF will have lost its ASW expertise for ever.
There are a number of degrees between Initial Operating Capability and Full Operational Capability and these have to be defined so that all involved are singing off the same hymn sheet. However, 3-5 years is indeed about right.
The window will be open or closed based on SDSR 15. If the govt of the day commits to buying a platform that can do the MPA role, then we're game on and everything will be ramped up accordingly. Conversely, if we just cannot afford to buy or lease the capability over the next 5 years, then I suspect SEEDCORN will rapidly become history and its anyones guess where we go from there.