The zincs wear away over time - once gone - the crab pot will slowly dissolve.
How long exactly is a guess but most will be falling apart in 3-5 years. A lot depends on the quality of the zinc and salinity of the water.
I some times bump into old crab pots diving and some literally crumble when I push into them. The rebar is still solid but the wire falls apart.
Sadly - often there are fish / crabs inside.
Zincs are also used on boats - these are replaced every year if boat is kept in water. Boats on trailers can get 3-4 seasons from zincs.
What could be more mundane than dying of old age or of natural causes when there is death by misadventure to be pursued ? Skip