I got this letter in early November, but just getting around to dealing with it today.
I am not sure about getting renewal details for such an important issue by email. I find it easier to overlook an email than a piece of paper.
It would be renewed automatically I suppose if one did not respond.
But I would worry about losing continuity of cover and therefore all the implications of that for medical insurance.
Although the letter said you must change your preferences within 5 days of the letter, I did this today without any problem.
Brendan