The collective controls the lift, or rotor thrust. The throttle(s) control power to the rotor to maintain RPM. Typically they are interconnected . i.e., pulling up on the collective advances the throttle(s) and vice versa.
As far as loss of collective control, in most cases one would simply fly as if it were a fixed wing aircraft. If it happened during cruise, as was probably this case, a safe touchdown can be done by doing an approach down to a height of maybe 10 or 15 feet above the landing surface, then decelerate by pitching the nose up rather high, then level off and let it settle in, chopping the throttle as it does. Not much difference than a full autorotation landing.
