Your question is unclear. I'm guessing you are a relative and are pondering whether adoption would be possible despite the fact that your relation's parental rights have been terminated. I'm going to answer the question with that assumption.
If the appeal is filed and successful, the appeals court will send it back to the trial court for reconsideration. If that trial goes well and no parental rights are terminated, then it is as if the original termination never happened.
IF the trial goes poorly and/or the parent loses on appeal, then the parental rights remain terminated. This means that that person has no rights in the child's life, including custody should the other parent die. If the other parent dies and you are willing to adopt the child, you may still be the adoptee if you are the best candidate for the child. The court will always consider past relationships and it is not as important that the parental rights of your relative were terminated so long as you can show you would be a responsible and loving caretaker, and one who would raise the child mindful of your relation's lack of parental rights.
In a California Juvenile Dependency case, the filing of an appeal after termination of parental rights does not effect placement of the children.
I think you are referring to the "Relative Placement Preference" (you can Google Welfare and Institutions Code section 361.3 to take a look at the statute.)
The case law says - "preferential consideration shall be given to a request by a relative of a child for placement of the child with a relative."
However - that preference fades with time - the longer the relative waits to request placement - the longer the child remains in the care of a foster parent and potentially bonds with that parent.
The preference is lost when it is no longer in the best interest of the child to remove them from a placement where they are bonded to the caregivers.
Your parental rights have been terminated - so it is likely the time to fight for relative placement is long gone. The only thing that will make the preference resurface would be if the minor(s) are moved to a new home - any time there is a change of placement - the relative placement preference kicks in again.
In a Juvenile Dependency case - family must act quickly and decisively to request placement of minor children - otherwise the family risks losing the children to the system.
So again - in answer to your question - the filing of an appeal has no effect.