Humans can't fly.

The battle against the Ragnarok Heralds continued, and the longer it went the more Valkyries lost their lives. 

Each of the remaining three monstrosities was adamant on reaching its destination and to do so they rained destruction on everything they passed. 

Though Sam had managed to convince one of the enemies to allow him to meet their leader, nothing was said about a ceasefire. That mean the battle will continue until he manages to convince the Nephilim queen to put an end to it, if that's possible to begin with. 

After all Mjölnir was just acting according to her own thoughts. She was sent to investigate the forty sixth base which was responsible for the use of Baldr's light, and though there hasn't been any specific orders, she was supposed to dispose of all the humans that were there.

No one expected her to come back without killing everyone there let alone bring the leader of the humans with her.