I relinquished my rights and my mother has adopted my children. If something were to happen to her, can I get my children back?

Anything is possible but I cannot render an opinion on the facts presented.

The best way to make sure that you do is to have your mother have a Will drafted stating that you will become guardian of the children.

No. Legally you do not exist until you re-adopt them.

If she dies and her estate planning has you down as guardian maybe you could get custody but if child protective services gets in involved they will probably stop you. You gave your kids up for all time and have no right to them any more.

Probably not, unless she has designated you as the guardian if she dies or you can prove to the court that it is in the best interests of the children for you to be their guardian.

Maybe, maybe not. Your parental rights (and I presume also the parental rights of the other parent) were terminated at the time of the adoption, which is to say that the adoption caused you and the other parent to become legal strangers to the child. The other parent is now a legal stranger and has as much rights as me or the next person to the child. In your case, however, you are actually your biological child's legal sibling, meaning that you and your biological child now have the same legal mother. Therefore you are a legal relative of the child. The real answer to your question is "it all depends." What it depends on is who the contestants for custody are after your mother's death. If the other adoptive parent (that would be your father or perhaps your mother's spouse at the time she adopted the child) survives the death of your mother, then he is the person who is presumably entitled to custody, but that presumption may be rebutted. The standard by which the presumption may be rebutted, as a matter of federal constitutional law, is whether the surviving parent poses a harm or threat of harm to the child. If so, then the State may interfere with the parent's right to raise the child as he pleases without interference from the State. (Here the court is the State.) So, in a contest between you and the surviving adoptive parent, you start behind the eight ball in having to show that the surviving adoptive parent is or is likely to be harmful to the child's welfare. If the contest is between you and a relative other than the surviving adoptive parent, then you and the other relative start on equal footing and the standard by which the court will have to make a decision is the best interest of the child. If the contest is between you and someone who is not a relative, including the other (former) parent, then your opponent starts behind the eight ball. Thus, in a contest between you and the other (former) parent, you would have a leg up as a relative. All of the above assumes that there has been no previous interference by the State with parental rights, meaning that the executive branch of the government (Dep't of Family & Children's Services) took the kids away and the Juvenile court rubber-stamped its approval on that action.