My question involves adoption law for the State of: Tennessee

Hi everyone. I'm specifically looking for someone with knowledge of Tennessee law. We do currently have an attorney hired, but I just have a few general questions.

What happens in the state of TN if a defendant party does not respond within the 30 days given to a petition for step parent adoption and termination of parental rights?

To give a little background behind my question: My husband is the primary care provider for my step son (I usually say son but for legal discussion, he is technically my step son.) My step son is 5 1/2 yrs old and my husband has been the primary care provided for 2 1/2 years. At this point his biological mother has not had any contact with him in 6 months (It was sporadic before that), and since the date child support was actually set in December 2011 she has made no payments or effort to provide anything. She is around $3600 in arrears. We kept visit records, phone records, and pulled all bank records for the last year and half. So we know we have grounds for termination in the state of TN. She was served with the paperwork, and as of now has still not made any attempt to contact him nor has a response been received (Although, directly after being served she did say she was going to fight it) So what happens if she doesn't respond? ....on the other side, if she does respond and tries to fight it..what is looked at for "Best interest"? She is living with and engaged to a man with a criminal history that includes domestic assault ..who is in the last court order as someone who is not allowed around my step son. We have proof of it all. We also have a notorized letter from her mother that says he is not safe with her and that she has a drug addiction problem.

Thanks for all answers! I know every case is different so i'm not looking for concrete since there's no way to know how a local judge will handle things. Just looking for generic information.