Sort Sale on home child support lien?

My son's father owe's me over 7k in arrears for child support and he decided to sell his home he just bought in 2009. He is taking a lost not a gain in the selling because of a sort sale. My question is can he still sell his home even if there is a lien on the property? I mean he is getting nothing back from it. His mother told me he can still sell because he is not getting any monetary gain from it. From my understanding when they go into escrow will they stop the offer from him to clear up his mess or will the still proceed...