EASA will have the power to stop national licenses and ratings.
I suspect you are correct.
However, I have read comment that whilst they will certainly be able to withdraw recognition outside the UK, it may be more difficult within the UK. Mind you I dont know the basis of this comment and I suppose it may turn on whether the CAA retain any authority over the sovereignty of our airspace (whcih you might expect they would). Whilst this is not a lot of help to CAA lifetime licenses (unless you never intend to fly outside the UK) the IMCR was always a national rating and therefore this element of the restriction would remain unchanged.