What happens when allograph tissue material is placed between my gums and teeth roots and it does not work due to the thinness of my gums?

Evaluate. If the bone plate is thin, you may need a block bone graft instead. Get another opinion.
Alt treat may work. If donor allograft material was placed to enhance or help provide a protective layer of gums over your exposed root surfaces, and the graft does not take, you may want to consider a graft of your own (hard gum) attached gingiva. While more invasive, a small strip from the roof of your mouth, or a sliver slid over from a nearby healthy area, may have a better chance of success.