Why keeping HMS Renown after 1945 required an almost total rebuild

How could HMS Renown have been retained in service after the Second World War?

Only through an extremely deep rebuild replacing most of the worn machinery and structure, a cost that made preservation far more plausible than continued service.

By 1945 Renown had accumulated the wear of service in two world wars. Continued operation would require an Anson-style reconstruction so extensive that little beyond the name plate might remain. A smaller navy such as Chile would not have the resources to sustain that burden. Renown nevertheless ranks with Warspite, Illustrious, Formidable, and several Tribal-class destroyers among the Royal Navy ships most worth preserving as museums.