The expiry of a delivery protects security and storage, but it must never erase your own administrative trace. In case of an audit, a dispute, or simply to find a supporting document, you have to be able to prove what was delivered, when, and to whom.
Separate the active delivery from the administrative archive
The delivery (the link the client sees) and the archive (your internal trace) don't have the same lifespan. The first can expire in a few weeks; the second is kept according to your accounting obligations (generally several years in France for commercial documents).
What to keep, precisely
There is no need to keep the files themselves indefinitely (your master copy is enough). What matters for the administrative side: the delivery date, the client's name, the project reference, and ideally proof of opening or approval.
A history that outlives the link's expiry
The right reflex is to choose a tool that keeps a trace of every delivery even after the link has expired for the client. xFer keeps the history of each delivery (date, status, approval) in your dashboard, independently of the link's own lifespan.
In short
Client-side expiry and administrative archiving are two different needs: never let the first erase the second. Keep a dated trace of every delivery, even once the link itself has disappeared.