From the Boeing 747-400 non-normal QRH for 'Gear tilt'
Do not retract landing gear
Observe gear extended limit speed (320/.82M)
Do not use FMC fuel predictions with gear extended.
This is makes more sense than an a/c departing with a nose-gear locking pin still in place and furthermore justifies the need to divert back to an airport capable of handling a serious delay (with passengers) and having good maintenance facilities available.