I dropped my diamond ear ring down the drain in the bathroom sink. Can I retrieve it? Could it still be there?

Don't use the sink or you will flush it through the P-trap!

Assuming your hubby loves you very much, your diamonds are big, and heavy. :D Based on that assumption, it could still be in your sink trap.

But seriously - do this: Get under the sink, disassemble P-trap. Take it out of the cabinet and pour water out of it to a container. Your diamond should be / could be inside the trap.