Can you please explain why you want to keep the data flows after it got completed ? We need to evaluate this to see if we are missing any product feature. This is a default clean-up provided by Pega Marketing / CDH to delete it. Otherwise it could lead into other performance issues including the landing pages taking a lot of time to load.
If it is for temporary debug purposes and would be toggled off, there are options to enable it through debug configurations depending upon the release you are on. It's highly recommended to leave the default clean-up as is in PROD type of environments.
As Sriram suggested, it is not recommended to override PEGA OOTP marketing rules for some benefits (like easy upgrade, hotfix release etc).
If you still need to keep the autogenerated data-flow, there are two options
All the failed data-flows can be tracked under Batch-DataFlow landing page. If your goal is to get the batch dataflow, make the campaign fail with incorrect inputs (add 1 sample audience as customer with incorrect inputs. This should be done with the help of Solution Architect/LDA)
Override few OOTP PEGA Marketing rules - Eg. BatchOutputConfig page params related to retaining the autogenerated dataflow available under CreateBatchOutputConfig Activity.
Hope this helps!
Nanjundan Chinnasamy | PEGA Lead Decisioning Architect