In fact, kdesudo-trinity does a dpkg-divert of normal kdesu. That 
reverts when it is purged.

You should be able in any case to run a (non-Trinity) app as root with:

su-to-root -X -c application

or use gksu (you don't have to install Gnome for that)

If you want your user disabled altogether from sudo you need to edit 
/etc/sudoers.