I can only answer for what might happen in the State of Texas. If you live outside of Texas, please ignore this answer. Family law is dictated by each state.
As a step-father, you have no legal standing to do anything.
However, the mother of the child has the legal standing to go after the child's father.
If he was ordered to pay child support, then it will be a debt that never goes away. It cannot be discharged by bankruptcy. The debt becomes the debt of the estate when he dies. The debt can be listed on his credit report to prevent him from buying a home. He can even lose his driver's license.
If child support was never set by a court, then your wife should do it NOW. It needs to be done before the child turns 18.
If you don't have any money, go to the Texas Attorney General's office in your city. They will help you for free. If he lives outside of Texas, then Texas will contact the state he lives in and that state will try to help you.
Some counties have free services to help you collect child support. In Harris County the Domestic Relations Office take cases.
Even if he does not work, most courts will order him to pay child support based on a minimum wage job. Child support will be based on the number of child he supports. If he has no other children, then you could anticipate receiving at least $150 per month in the State of Texas.
If he is disabled and unable to work, the child might be able to receive some social security benefits.