I just harvested... Can I leave it with just branches and put it under 24/0 light and will it go back into veg?
It can with some time. Iv done it but time wise starting new plants is way faster. If you are wanting to preserve the strain then Do go for it.
Just give it time, it will regenerate. I suggest googling "Re-vegging" That should bring up some more info, I personally don't do it.