As you read on other threads, you can't undo an adoption. But you could be readopted by your bio-father.
Please, a "re-adoption" is NOT the same thing. He needs to be adopted by his biodad (which would make biodad the SOLE parent. Biodad NEVER "adopted" the poster, so this would NOT be a re-adoption. Just as one cannot undo their bioparentage if they fall out of communication with a bioparent, they can they undo adoptive parentage.
My daughter was "readopted" and it had nothing to do with bioparent or undoing an adoption.
Just an FYI. THIS is readoption. It has nothing to do with reversing an adoption:
http://www.jcics.org/Readoption.htm
Readopting Your Child From Overseas
Under US Citizenship and Immigration Services (CIS) regulations, children who were not seen by all relevant parents prior to their overseas adoptions are not considered to have full and final adoptions. They must be readopted in the state where they will be residing. This rule applies even in cases where the foreign country considers such adoptions final. One implication of the US CIS position is that children who were not seen by all relevant parents prior to their overseas adoptions cannot be considered automatic citizens until readoption occurs. Children who were seen by all relevant parents will have been issued IR-3 visa and will be eligible for automatic citizenship. Children who were not seen by all relevant parents prior to the overseas adoption will have been issued IR-4 visas, and are required by US CIS to be readopted before becoming citizens. Once a re-adoption is completed in a State court, parents can request a birth certificate be issued from the State's Department of Vital Statistics.
Although US CIS does not require readoption for children who were seen by all relevant parents prior to their overseas adoptions, and who traveled home on IR-3 visas, Joint Council recommends readoption in these cases. One reason is that U.S. adoption documents are much more easily replaced than foreign ones if they are lost or destroyed. They are also more recognizable by schools and other organizations to which they may be presented. In addition, readoption may make it easier for families to change their children's foreign names and to obtain state birth certificates for them. Some attorneys feel that readoption could help to protect a child's inheritance rights.
Readoption is a state function, and procedures are not uniform among the states. Parents may obtain information about readoption from their state court system or via their Joint Council member local service (homestudy) agency or placement agency. Families should recognize that some states have readoption requirements such as post-placement visits and/or the updating of some documents, such as child abuse and police clearances.
In some states, procedures for readoption are fairly simple, and a family may feel that using an attorney is not necessary. In others, using an attorney is advisable. Local service agencies may be able to provide the names of attorneys familiar with readoption cases, but families may also contact their State Bar Association or the American Academy of Adoption Attorneys.