If I read this aright, the UK PPL will still exist, its just that it won't be renewable by instructors/examiners.
The UK PPL will only exist for Annex II aircraft. These are aircraft that are not under EASA control, old aircraft and UK permit aircraft that do not have any EASA documentation and of course Microlights.
If you want to fly EASA certified aircraft you will need to SWAP your National PPL for a JAA PPL. The JAA PPL will be accepted as an EASA Part FCL licence. Its a paperwork and money exercise if you do it early i.e. before April 2012. If you wait, there may be additional conversion requirtements.
UK Instructors/Examiners will be able to perform all the usual functions on either licence.