That's why prophecies about death are bullshit, and in fact why prophecies in general are bullshit (which also addresses your point later) They can always be interpreted enough multiple ways in that they're right almost no matter what happens. For example the prophecy was right because Diana took down the League is just as valid interpretation as any. Which is why depending on prophecy to be right in the way that you think it means is never a good way to go, because each of those stories is generally about how somebody thought they new what the Oracle meant and fucked up bad.
As for the Balefire, Wally would never be hit, Kyle's ring would most likely protect him, J'onn would stay far away cause y'know, fire and all, Supes would also probably be able to dodge. The only one in danger would really be Batman, and he has enough experience getting out of the way, he'd probably have an advantage there as well.
Which brings us to a larger point. Why isn't it their call to make? Why does Diana get to decide when they put themselves in danger? They've faced certain death countless times before (even in front of Darkseid, as has been mentioned) why is this different? And if Diana doesn't trust Superman, her oldest friend etc etc to watch her back, why should anyone believe she trusts anyone else?