In my opinion it would be ready to be chopped down. That plant has gone through way to much shock to really get much more benefit from it. Learn from the experience it happens. Now it could end up being a great smoke, but personally I wouldnt of waited 18 weeks, thats a struggle to keep it alive even during flower that long. Im sorry the plant didnt do so well there but perhaps implement some more cfl lighting or just go out and get a 400 or 600 watt hps/mh you will be much happier in the end..always outdoors if you got no cash.