Now it seems that Mechanical Desktop is really at its end of life (see an older post). MDT 2009 should be the last released version – and this version will be available for download also to all users of future Inventor versions.
Future Inventor versions will be still able to import MDT data (DWG files) so you can reference and modify your past designs. Service packs, updates and support for MDT will be available for a couple of years.
I don’t think this burial will affect many users – almost all MDT users have already switched to Inventor or other modern 3D modeler.