in the medium containing ampicillin and tetracycline, the growth of the recombinant DNA will cease and the growth of non- recombinant DNA will continue....then how will the recombinant DNA be isolated from the mixture????

Recombinants will die if they are grown on the medium containing the same antibiotic, within the region of which the foreign DNA has been inserted in cloning vector while making recombinant DNA. For example, a plasmid has resistance gene for two antibiotics such as tetracycline and ampicillin tetR gene on a plasmid has BamHI recognition site. When BamHI is used for restriction, foreign DNA fragment is inserted within the tetR gene. Hence, tetracycline resistance is not present in those recombinants. 
        Recombinants will grow on the media containing ampicillin, but will die on the media containing tetracycline.On the other hand, non-recombinants will grow on medium containing ampicillin as well as on medium containing tetracycline. In this way, insertional activation is used in the selection of recombinants.