What happens if you don't respond within the 10 day window of receiving the recall letter?

I received the call but just let it go to voicemail and Comair still has an old address for me.

I'm not planning on taking the recall, just wondering what happens if I don't respond.

Also is there anyway of getting a refund on the Travelnet access ($50) or keeping my flight benefits if I don't take the recall? I just paid it 2 months ago... Thanks.