ABAP - program versions after S/4 upgrade

Hi SAP,

we are in the process of preparing for S/4 HANA upgrade (on premise).
Per SAP guidelines we are following CCLM process and decommissioning obsolete code from our landscape.

A question has arisen we regard to deleting custom programs:
Currently, in our ECC landscape, if we delete a program completely from DV/QA/PD systems, the old versions of the program still exist (archived in some way) and if for some reason we need to bring back a program, we can pull one of the old versions in DV and move it back to QA and PD via a transport. (UN-delete it in essence)
We can still see versions of the program right back to the beginning of our system (20+ years), across multiple upgrades over the years.

As S/4 is a whole new approach, can SAP please confirm that once we go to S/4 that older versions of custom programs (pre-S/4) will still be available in version management?
This is a simple question but is important to clarify, as we are removing as much "obsolete" code as possible, but it could be the case that some programs are still needed - we would like to know that we have a way to bring them back (as we do today)

thanks,