Currently it is not possible to continue on after a disconnect if the client is behind the purge seqno. This situation is common in flaky network environments, such as WAN, links, and effects the feasibility of collecting a full backup from a large data source.
This issue is expected to be hit when backing-up to cloud.
A possible solution is to keep the file handles open after a disconnect for a short / configurable period of time. Then if the client re-connects with the same DCP stream and details (e.g. end snapshot) the stream can continue where it left of, using the old file handle.