BL:-
In terms of temporary work, to deal with individuals then you need a pilot to be under the employment of a company willing to engage in sabbaticals
Why? My guess is (and it's only my guess!) is that BA will be up and running well before MFTS is, though many other companies won't be (some possibly never). In that case BA (who I suspect will be topping up the salaries of their pilots who are detached to the RAF) will want them back well before the RAF wants to release them. How will that be resolved, in BA's favour or the RAF's? Better to deal with individuals, from BA and elsewhere, who are on temporary contracts which will cease, minimum notice not withstanding, when the RAF so decide. Unprecedented? We live in unprecedented times! No-one would accept such terms? Faced with the possibility of ending their flying careers entirely I suspect many will take a punt on a second RAF flying career that could well continue for some years and well beyond any planned sabbatical timescale.