It might well be just the selector lever, I think your mechanic mate could be right.At the back of the g/box there is a rod from the gear lever to the gearbox selector output shaft.This rod is splined and held in place with a pinch bolt.If the pinchbolt was loose the jolt of stalling could have caused the splines to become missaligned hence no gears.
My mate got his R back from havin a clutch fitted and some times the car stayed in gear with the gearlever in neutral.Got it into my workshop and took the selector rod off moved it round a spline problem sorted.
Hope this is your problem and not a broken selector in the box.