After my site gets indexed my search engines should i take down my mega tags. Yahoo doesn't have mega tags.

No, leave them in there. Search engines don't crawl your site only once... they may come back.

And meta tags are used not only for search engine indexing. So leave them

If your site is indexed in yahoo.com. it does not means that all search engine search your site. meta tags should be there because some search engines refer to meta tags and some engine does not refer to meta.

To index your site. dont take out meta from your file.

regards,
rakesh.
http://www.logixsoln.com