Under Settings -> Time and Language -> Text Input -> Installed Input Methods needs to have something in there "English UK" for example. I turned off the phone. Left it for 10 seconds and turned it on again and it worked! The keyboard was back! Somewhere in there was the problem.. not sure what did it but I posted this up in case someone else out there lost a keyboard whilst playing with their Nokia N9.
Touch screen devices now mean we can never take the keyboard for granted
@NokiaHelps on Twitter just left this message which may be helpful to someone experiencing the disappearing keyboard:
'Unfortunately not known why virtual kb lost. If still happens, try pressing power button for 8s to reboot'