Well, shit.
None of us in the library are in a position to really go back and help as that would more likely than not end up with whoever fights their way back and Balder dead.
I don't know if Melis would be able to go back but even if she was, her Agent would follow and we've already shown that trying to take on two Agents like that doesn't work terribly well.
The only thing I can really think of that could work is if the three that are with Balder team up to get that Agent vulnerable quickly and then Helios throws him. Helios, Hawk, and Balder are not the best fighters in the group by any means, but at least the Agent's attention would be split and if Burn kept up heavy gunfire on it, that should at least keep the Agent's attacks from being too nasty, or possible from it attacking at all.
That's about all I can really think of to get out of this mess.