Well the burden shifts to an extent onto Romney and Ryan. Their detractors want to write a story about how Ryan isn't up for it, how he has an anger issue, and how he doesn't understand some mundane fact or the other. They also want to write the "They're back" narrative.
As long as Ryan stays away from that and the debate is a push then that's good for Romeny. If Ryan isn't prepared with attacks on 47%/etc. from Biden you'll get the "They're back" stories.