If you are successful getting bumped, you might ask to get a dollar value certificate rather than a free round trip. My experience with free round trips are limited availability.

I had a US Air certificate. Airfare where I wanted to go was under $200, but there was no availability with the certificate. I was able to call customer service and they exchanged my round trip cert for a $200 cert and it worked out, but you might be better off asking for the dollar value cert up front.