I am not an engine expert but if some of the rockers arn't moving, then you've got a big mechanical problem on your hand. The camshaft may or may not be the culprit of this, but it sure is in the valvetrain.
Did you hear any knocking, loud unusual engine noises, or when the car died, did it make any loud noises from the engine?
Yes, your friend could be very correct on his guess of the camshaft being cracked in half.
I personally don't think it would be the cam shaft though, because the way these things are built, they just don't break. It could be the rods though.
I do not want to comment on how to fix this, somebody with a little more 3800 engine knowledge will be better suited for this.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.