The samba audit logs in a database. I found log entries from 2017 so I don’t think there’s an autopurge. You may delete the logs from web UI.
http://docs.nethserver.org/projects/nethserver-devel/en/v7/samba_audit.html
http://docs.nethserver.org/projects/nethserver-devel/en/v7/nethserver-base.html#log-retention-and-rotation
I assume it will. At least there will be documentation how to update correctly.
I have to mention that XP is not supported anymore and is a security risk.
Here are some infos on XP:
Glad it works.