Sync Framework does not detect database or connection availability. Syncronization is something that you invoke or initiate.
In your case, you will have to code the part that detects if your DB Server is available. If it's not available, you can redirect all database operations to CF (inserts only since your CF doesnt have copies of rows from the server so there is nothing to
update or delete).
You can then use Sync Framework to synchronize this CF to the server (configure UploadOnly sync direction) to upload the changes when the connection is restored.