As recently noted, the official 3D Realms website currently has a 'Goodbye' post with a picture of the full Duke Nukem Forever team inside the company's Texas offices.
However, 3DR representatives have made the following statement regarding the developer and the lawsuit circumstances, claiming the developer will continue to exist as a much smaller entity:
"In light of recent press articles and statements by Take-Two (to the media and in a lawsuit), we want to set the record straight on some issues.
Despite rumors and statements to the contrary, 3D Realms (3DR) has not closed and is not closing. 3DR retains ownership of the Duke Nukem franchise. Due to lack of funding, however, we are saddened to confirm that we let the Duke Nukem Forever (DNF) development team go on May 6th, while we regroup as a company. While 3DR is a much smaller studio now, we will continue to operate as a company and continue to license and co-create games based upon the Duke Nukem franchise.
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http://www.gamasutra.com/php-bin/news_index.php?story=23681