I thought it was a trick question.
I believe the NPPL SLMG licence will disappear completely.
The CAA allow SEP licence holders to fly SLMGs within UK airspace (& by that they mean the NPPL definition of SLMG) so we can all fly Grob 109s, Falkes, T61s etc without a TMG rating. The EASA PPL(a) will continue that privilege:
The privileges of the holder of a PPL(A) are to act without remuneration as PIC or co-pilot on aeroplanes or TMGs engaged in non-commercial operations.
What we can't do now, nor will we be able to, is count TMG hours towards the minimum required to revalidate your SEP class rating. You need an actual TMG rating for your TMG hours to count towards both your SEP & TMG rating revalidation.