All loose-fill insulation settles after installation. S&N Cellulose is always specified and sold at settled density. This means that settling has already been compensated for in the bag count and material weight columns of coverage charts. This may, or may not, be the case for other loose-fill insulation.
Neither Stabilized Cellulose or R-Foam insulation will break-down or decay with age, and should last the life of the structure, under normal conditions.