I think there is some confusion here as there are two totally separate subjects. Firstly non use of Turkish simcards....there was always the possibilty that your simcard provider would cut you off if your phone was not activated for some time, it was luck of the draw because sometimes it was done and others not....there is nothing to suggest that this situation is not ongoing.
Secondly there is the question of registering your turkish simcarded UK phone. As previously there seems to be no firm information as yet as to what exactly is happening other than yesterday was supposed to be cut off day. My own mobile was registered and is still working. It also seems the site where you could check the registration is no longer working. I think it will be a wait and see what happens situation.
With regard to keeping your simcard open send a text say once a month to a Turkish number....very low cost and should avoid deactivation, but remember to ensure you have credit on the phone.