Hi Dina. While that might be ideal, in pratice it's not usually possible and Tableau don't expect you to have to do that. We've literally just upgraded from v9.0.3 to v10.1.1. We have over 200 published data sources, 1700+ workbooks containing 6000+ views. To republish all of this content would just not be achievable. Tableau provides the ability via tabadmin to restore content from a backup which we use as part of our upgrade process.
Agree with DONNA.
If there's no compatibility issue, I will not consider republish.
Especially "Connecting to Tableau Server-based data sources" part.