No, on the contrary. The certificate and proof of registration that you obtain when you register are valid for life, to prove the date and time you registered your declaration of authorship or rights, as well as the identification of the work. They do not expire or lose their validity, regardless of whether or not you remain a Safe Creative user.
In addition to making timely registrations, Safe Creative also offers subscription options, not because it is necessary to contract them in order to maintain the registrations, but because they allow professional users (designers, composers, editors...) or corporate users (publishers, representatives, lawyers...) to make unlimited registrations, providing them with a very economical way to protect their entire production, including sketches and intermediate work phases, or that of all the works of the clients they manage.