"now" could benefit from some definition though....
Commercial RHI was rolled out 2012 (from memory), domestic RHI 2014ish.
At that time we were still well and truly under the oppressive yoke of EU domination and whilst the avoidance of punitive fines may have been a strong driver for such incentives....
Roll forward to 2016 referendum - where the MAJORITY of the UK decided to say FU EU for a wide and varied number of well considered, deeply researched national and personal interest reasons...
And here we are at the curtain call of 2019 and the process of 'leaving' the political union of federal Europe is only just starting to gain traction.
So for domestic RHI with a 7 year term, 2021 sees it coming to a close anyway for the early entrants. That said, and as can be applied across the ENTIRE spectrum of (soon to be former) EU compliance, UK national processes (many of which far exceeded the minimum standards imposed by the EU) will stay EXACTLY as they were before UNTIL, by act of parliament, they are changed to a more tailored solution.
Planes will still fly, manufacturers will still manufacture, sellers will still sell, buyers will still buy, medicines and foodstuff will still flow backwards and forwards.... All in exactly the same manner as they have done for generations and the likelihood of plague, pestilence, riot and disorder will quietly be forgotten - most embarrassingly by those that tried to convince the gullible that the world would stop turning the day after the EU referendum.
So, yes, we ARE leaving the EU and the 'requirement' to comply with EU emissions directives will cease to apply. Should that be read as meaning RHI / solar PV tariffs etc will immediately slam into a brick wall? Personally, I anticipate UK national requirements will exceed current EU directives and therefore the incentive to encourage roll-out of renewable systems will increase - but that increase will be UK initiated not for fear of incurring punitive EU fines.
(for Mull) The short answer is yes, we are (finally) leaving the EU. It doesn't make any difference...