Its hard to say when its down by your liking as you need a loop to check the trichomes for the colour you want. If you go by the colours of the hairs you look over 60% so by the time you flush the plant it should be done by then i would say a week to two weeks your done. As for re-veg it will work but know its going to take a long time to re-veg just be patient all in good time it will bounce back, I wold not worry about toping the bud but thats me i don't think it will work at this time, your doing a good job nice work
I agree with Serpent... As far as re-veg, I would not attempt that at this late in the stage... It is always possible but I have done it earlier than this and it was difficult... Takes a while a long while!... By the yellowing of the leaves (that's normal in this late stage) you are getting close... Like Serpent mentioned already check your "Trichomes" for desired medication...