When creating the request, you set a deadline. As long as the request is active, you can extend the deadline.
If the deadline expires before everyone has signed, the request is ended – as with a cancellation: all participants are notified, and the document with the signatures collected up to that point is sent to everyone with the «Receive» role. It is marked as incompletely signed. You can obtain the missing signatures with a new request; the expired request cannot be continued.