My take on this - not as informed as some others here - is that the LAPL will happen, and UK NPPL holders will get grandfathered into it.
I think the "NPPL medical" situation will also have to be carried forward, otherwise the majority of the UK NPPL community (which is flying on the NPPL because of CAA Class 2 medical issues) will be grounded.
And France has already accepted the UK NPPL, I gather...