Yes, at any time with the «Manage» role. Cancellation is final – the request cannot be reactivated.
When the request is cancelled, all participants are informed, and the document containing the signatures collected up to that point is delivered to everyone with the «Receive» role, marked as incompletely signed. If the document is already in the mailbox, a corresponding notification appears there. The signatures already provided remain valid – you can use them to start a new request with the missing people.