well, if you still have KDE installed, but not as you default, chances are that konqueror is still installed on you system. Theoretically, it is completely possible, although the browser may look a little different (I can do the exact opposite by running Nautilus in KDE). All you have to do to start it is to go to Run Command in GNOME and type
in order to launch Konqueror. However, unforutnately, I am unfamiliar with exactly how you change the default program for different file types, but I know you can do it in Gnome as well as KDE...