I received a reply from Telerik support. Below is the response...
Thank you for contacting Telerik Support.
Such scenario is not currently supported by Sitefinity 4.3. What I can suggest is to migrate each site ( as they share one database ) separately. You can follow our migration guide:
Basically you can use the Project Manager to install the Migration service, then you can start the new 4.3 project and follow the on-screen instructions.
the Telerik team
What I am not clear on is the direct question on whether running multiple sites from the same sitefinity databse is possible with 4.3. If it is not yet supported, what is the timeline on supporting this? The cost implications of having all of the sites have their own database on Azure is huge.