You have a simple choice - convert to a JAA licence before EASA implementation, in which case the transition is seamless, or don't, in which case your national licence becomes invalid
... and pay a fee and 5 year renewal.
I have a lifetime PPL issued by the CAA. As I read it, they can terminate this at any time, but should they?
It should be grandfathered across but of course that would be too simple for our CAA. They want UK PPL holders to demonstrate radnav skills or else we get an NPPL