I am in the process of migrating a site from table layouts to a pure CSS layout. The site itself is well established and ranks in Google and the migration does not involve any changes to site structure, page naming or content. Could an update of this nature cause Google to reindex the site and possibly drop it from the index, at least temporarily?
In my experiences, you will never get dropped from the google index because of this, not even close. However, once you have had a site that ranks for a few weeks or months for a "moderate or high" competitive keyword and go through a change this may cause your site to fall a few spots or pages in rankings .. at least it has for me. Because lately I have been scared to change a few pages and sites of mine because of the fear of changing layout and structure but to answer your question, google would never de-index you unless you spammed or something of that nature.
hey you can lost ranking if you change onpage seo factors.Its better to hire some web designer who have seo experience.I can help if you want.