By the sound of things your trans is already dead. If the shift linkage is properly adjusted & you have no reverse gear but the car moves forward in N then I can only imagine you have wrecked the overrunning clutch A.K.A the sprag in the rear of the trans.
There is also no neutral reverse band in there. Maybe your friend is referring to the rear band which is known as the low/reverse band. This could well be broken, or the rear servo piston is damaged but I have never seen one eat it's way thru a case.
I would first drop the pan & expect to see a few hard parts laying in it. But I would definately not drive an inch further with that trans.