If I understand correctly, those chemicals don't go away unless destroyed with highly sophisticated and expensive methods. They will continue to accumulate in concentration and cause more impact over time.
half-lives of long-chain PFAS were longer than those of short-chain compounds, reaching almost 3 years in some cases. Some studies estimated the average half-lives for PFHxS at 2.86 years and L-PFOS (a specific form of perfluorooctane sulfonic acid, C8) at 2.91 years. In comparison, the short-chain PFPeS had an estimated average half-life of 0.63 years, and perfluoroheptane sulfonic acid (PFHpS, C7) concentrations were 1.46 years. The shortest estimated half-lives were for perfluorobutanoic acid (PFBA, C4) at 0.12 years and perfluoroheptanoic acid (PFHpA, C7) at 0.17 years.
There's also a study from Europe showing vastly different half-lives based on soil temperature (colder temps -> longer half life), but I cannot locate the paper at the moment.
US EPA. (2014). Emerging Contaminants Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA), https://www.wqa.org/Portals/0/Government%20Relations/factshe... arch2014.pdf