How long does foam concrete leveling last?

The foam itself doesn’t break down. It’s waterproof, it doesn’t wash out, and nothing in the soil eats it. In practical terms it lasts as long as the concrete sitting on top of it, which for most slabs is decades. The honest caveat: foam fixes the slab, but if the reason it sank is still active, like a downspout dumping water right at the edge, that can cause new movement. Fix the water problem and the lift holds.