Cast iron's durability comes from its simplicity — it's a single piece of iron. If it rusts, you scrub it, re-season it, and it's as good as new. Pans from the early 1900s are still in daily use. The only thing that really shortens a pan's life is cracking from severe thermal shock (like plunging a screaming-hot pan into cold water), so avoid that and it will outlive you.