Hi Isla,
At The Open University, we're looking at Moodle Tool_Lifecycle to help automate some of our housekeeping. It'll still be very people- and process-driven, of course. We plan to auto-remove module presentation websites to a 'recycle bin' category about three years after they became read-only to students, but have our Moodle administrators confirm the final deletion of the website from our servers (possibly as a weekly check task). Nearly all module presentation website content is downloadable as EPUBs/PDFs for students, and all Moodle collaborative tools have export functions, so we feel that this 3.5-4.25 year life gives students adequate time to refer to or download anything they need. It also gives our library archiving services a good time window to archive any study content. Obviously all data the university is legally required to retain (assessment scores etc) is stored in our central systems as long as necessary.
Non-website-presentation-specific content, such as 'public' or general resource websites, user profiles, and personal blogs... we're still working out the details around those, as their 'start using' and 'end using' dates are far less clear.
Best wishes,
Chris Nelson
Digital Assessment (and GDPR) Development Manager, The Open University (UK).