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To answer the question: yes if it sank then the internals filled with water and the circuitry is now ruined.
Truthfully though it's not doing much less broken on the bottom of the pool than working on the top, those little things are basically a placebo which put barely any copper in to the water. However, you really don't want copper in the water because it's nothing but an algaecide that causes green staining on pool surfaces, hair, and finger nails. So now is a great chance to discontinue putting more metals in to your pool water.