I submitted a sitemap when I signed up for webmaster tools.  I
reorganized my site a month or so later that has left me with a lot of
404 errors (which I've submitted to google for URL removal).  It seems
even when I submit the URLs for removal, more 404 errors appear (some
for the same URLs I had removed).

Should I just delete my sitemap and then resubmit a "rebuilt" one (I
use a plugin for wordpress)?  Would doing so help remove all these
errors?

If not, under what circumstances do people resubmit sitemaps?

Thank you for your help.