Nothing grows back, when u top, u destroy the the cells in the plant that are responsible for new growth. However, every node/budbranch/budsite, has the same cells that create new growth like the top had before u cut it off. So, the new primary growth that used to be the top, now resumes on the 2 nodes closest to the top that were already there. All the growth is moved to the those 2 spots now, and u will have 2 branches that go up instead of one stalk. If done correctly and lst'ed u could get more yeild because more light hits the overall plant, so u didnt screw anything up, just didnt realize what u did. When doing topping u promot the plant to grow more "bushy" then "tall". So overall you'll get more consistent buds from top to bottom, opposed to have a big cola and smaller buds .