How long does your Enterprise Social Data (needs to) live?

The Internet does not forget, neither does Facebook. Before the rise of the social Intranet corporate policies were easy: When an employee left, a copy of the eMail (database) was given to compliance and then all existence of the gone member purged: the PC reformatted, the mail deleted and (eventually) contributions made as part of a corporate role assigned to the successor (typically in an ECM or WCM). With social media it isn't that easy any more. There are a number of interesting questions to be asked and answered:

• Should a user profile be kept as is (with the exit date added), deleted or reduced? The profile serves as the anchor for all the other entries, so a removal would result in a lot of "profile not found" errors. Eventually a reduction to: Name, time in corporation and last title/position and, if the employee agrees, destination makes most sense
• What happens to the network relations? Are they invalid when an employee moves on, after all there are two ends to it?
• Are status updates and their comments to be purged? Would comments made on my "wall" suddenly disappear when the commenter leaves? Would my comments disappear from other boards when I leave? This would "rewrite" corporate social history. Doesn't sound right to me
• Would blog entries be purged? Suddenly all incoming links became invalid. Quite often blog entries are referenced in "check this out, it describes what you need" ways. That knowledge gets lost if purged. Same question arises for blog comments
• For WIKI contributions the situation is even more complicated: what happens to entries entirely created by an leaving employee (delete them?), what with all the edits and what if they were the last changes made to a WIKI page, undo them?
• For files there are several categories: files uploaded, but never shared, files uploaded and made public, with the subcases: "never downloaded" and "downloaded" and files shared with someone specific. Should files be purged unless someone takes ownership? How would such a ownership handover look like? What about files shared in Extranet (e.g. LotusLive) settings?
• In communities I see the need for a "past members" section. When a user leaves the community (s)he can decide to be listed there, with the default to YES. The exit workflow needs to cater to ask the question
• Activities don't seem too much of a problem since they expire once completed, still orphan entries need to be avoided, so some orderly handover is needed
• How would one handle an employee coming back. This happens in IBM quite often. Sometime through an acquisition, sometimes through regular hire. Common practise today (in IBM) is to get the employee ID back. Should that hold true for relations, communities and other social data?
• What is the right balance between keeping and purging? Purging leads to "corporate Alzheimer" while keeping costs money and effort and increases cost and risk for a legal discovery phase

All these need to be checked against national privacy laws, signed agreements (depending on country eventually driven by employee representatives like a union), compliance requirements, potential discovery cost etc. Interestingly for source code that question has been settled: you leave, your code stays. I see happy smiling lawyers at work.