How can cell death continue almost indefinitely, even after prevention of further exposure to silica dust or asbestos fibers?

This is because the silica dust and asbestos fibers inhaled will stay in the lungs for a couple of years even after leaving the area of exposure. The dust and fibers will continue invoking immune response (engulfment by macrophages). This response result to production of collagen and extracellular matrix by fibroblasts. This cause formation of nodes in the lungs (due to cell death) and spread from the lungs to other regions (confluence).

do you have a picture?

the answer to your question is sperm