The main thrust of the question was what happens to self-isolations still under way when it gets to the date that no new self-isolations will be required.I haven’t read the whole thread and I’m relatively new here but I would say, if you are pinged or contacted by Test and Trace please do isolate and for the entirety.
I‘ve ran too many codes and called TOD on too many people that I couldn’t stand 1 more death that can be avoided, happening.
(and specifically for one or more questioners, being double jabbed and only two days short of their end date)