You could flower and re-veg it without harvest, but that will be time spent if maximal veg. is your focus. Another option is to flower the plant and then clone the flowering plant, but re-veg the clone. It will re-absorb the bud for root growth. OR still yet, re-veg the entire plant. Any way you look at it, there are options. But yes A plant needs to flower to show sex. In truth, some of the biggest bushy yields I've seen have been re-veg'd. Cool stuff.