This is not the usual Ctrl-M hide-show problem.
I enabled the xbar widget which extracted the menubars from all KDE apps (Konsole, Konqueror, Okular, etc). I am (was?) also using bespin style. But it did not work all to my liking, so I removed the xbar widget. I assumed the menubars will happily return back on to the windows, but they didn't. I tried logging out and in, enabling and disabling xbar multiple times, changing the style to oxygen, adding macStyle = false in .kde/config/kdeglobals file (under KDE section) (and logging out and in after that), removing the xbar widget package altogether, etc etc (whew!!!!) but still the menu bar hasn't returned .
I am able to get it back if I start with a fresh .kde directory, but I have a lot of customisations done like positioning my news widgets, icons, themes, etc so dont want to start all over again. I know it's somewhere in there in the .kde folder but I am not able to get the right setting to enable the menu bar (macStyle doesn't work).
Anybody knows a beter solution than to start with a fresh .kde directory?

Found the solution at last.
Did a "grep -i" for menubar in .kde/share/config directory, and it came up with 2 files konsolerc and systemsettingsrc that had "Menubar=Disabled". Removed the 2 entries and the menubar is back where it belongs. (I guess the konsolerc entry got in there while I was fiddling with the "show menu bar" context menu option in konsole main window, but the main culprit was the systemsettingsrc entry which disabled the menubar in all kde applications)

Note that System Settings forcibly disables its own MenuBar, it is not possible to enable it, however it should never be able to affect other applications.