I probably don't know more than you, but I am interested in learning more about it. The insulation most often used is EPS (expanded polystyrene), which many studies are trying to find ways to accelerate decomposition from an ecology perspective. Sheltered from UV and solvents, it should last more than 200 years, with some marketing materials giving it an indefinite lifespan. We need more history on ICF, since it is a relatively new building material/technique.