I'm experimentation with embedding my pure offline mobile HTML5 e-book readers (http://www.hyper-books.com/) right into a UIWebView. Why? I wish to find out if I'm able to hands off certain durable try to native iOS, lock the orientation of site with the application container, entirely be rid from the status bar and integrate using the twitter framework.

The applying is storing all of the data inside a html5 database. Therefore the following problem entered my thoughts: Will the html5 database connected using the UIWebView be flushed if the application update happens on the telephone?

No. The database cache is saved within the Library/Caches folder, that is maintained when an application is up-to-date (unless of course the consumer removes the application before upgrading).