If this was the case where I worked, I'd be responsible for the WF copy of the document, but whomever wanted it pushed to SharePoint (I assume this is for an integration?) would be responsible separately for that copy.
If this is NOT an integration and instead is some IT demand to store the doc in two places, then I might be responsible for managing both copies. Though I would push-back on IT to manage their copy.
Be that as it may, WF has no document retention tools. We have a similar policy where projects must be removed after a certain number of years and we'll need to have a procedure to do an annual audit and manually delete projects (which deletes the documents attached to it, as far as I know).
I was exposd to this can of worms a couple years ago when "Information Governance Liaison" got added to my many hats for our group. Real eye-opener how much Legal needs to track and do and how few tools (like WF and DAMs) even take long term data deprecation and deletion into account. Makes it all far too manual.
Maybe this is something Fusion could handle?