Is there any way to go back and identify, retrieve saved sermons from before the new version?

If memory serves correctly, downloaded files should have been retained during the upgrade. However, play progress wasn't. But, if you aren't seeing those, there is no way to go back and get them.

We are currently working on user accounts which in the future means you will not loose anything if you upgrade or delete the app and reinstall and it will sync all your devices that are running AC Central if you are logged in.