In reality, even if the high levels of the Human Race didn't agree to those conditions, the Angels wouldn't just let the Humans perish. Because for those Angels, the Humans are the foundation of their existence in this world, and unless absolutely necessary, even without any benefits, the Angels would protect the safety of Humans.
It's a pity, however, that the high levels of the Human Race didn't realize their importance to those Angels. So, when they encountered a major crisis, they immediately decided to pay a huge cost to ask for help from the Angels. Otherwise, given the nature of the high levels of the Human Race, upon knowing their importance to those Angels, they might really have chosen to do nothing, just sitting idly by as they fell behind, forcing the Angels to join the battle.
