Now that I think about it, Hawkgirl's completed her mission too! While most people (Including myself) were busy pointing out that Max Lord and for some reason Jade already completed their missions, complete with the White Lantern telling them so, and that Aquaman has technically completed his by finding Aqualad who the lantern only told him to find; we're forgetting that Hawkgirl's mission was to save Hawkman from Hath-Set. Hawkgirl KILLED Hath-Set. I'm pretty sure that qualifies. 
Conversely, Hawkman MAY have failed his. His mission was, 'Don't let them escape Hawkworld, stop The Queen. THey could still stop Queen Shrike I suppose, but she and the others DID escape from Hawkworld. So did he half fail or something?

You think they revive people like vlad the impaler, or Jone of Arc after this is over. How about a gun fight between Sundance Kid and Jonah hex?    

" I have mixed feelings about Boston, Hank and Digger. If any of the 12 fail, I have a feeling that atleast 1 of the 3 will. 
 
I put some thought into it and came up with this idea

SPOILER WARNING: Click here to reveal hidden content.

The final issue will see Digger succeed in his mission, Hank and Boston will fail. During the final confrontation, Digger will throw the boomerang at Dove. Hank will miss the boomerang by mere centimeters and in response to Hank missing his chance, Boston with his ring drained of it's power, will either:  
 
A.) Shield Dawn by trying to charge his ring infront of her, holding the White Power Battery up infront of himself. The battery shatters (due to the fact that Digger's boomerangs are Black Lantern like constructs) which causes it to turn to ash and Boston fails along with Hank (Thus the ash from the picture above and Boston seemingly loosing his power). Despite Dawn's pleading, Hank and Boston both say their goodbyes and explode into white ash and the Entity explains why Hank and Boston can't return as the story comes to a close. 
 
B.) Try to use his ring, disreguarding the fact that it's drained. But, realizing his mistake too late, Dawn is killed by the boomerang. The Lantern then speaks to Boston, telling him that he had failed his mission to await for the savior. By allowing Boston visions of the future that would've been, it's revealed that Boston had gotten Dawn pregnant, their unborn child being the savior. Boston, in shock and on the edge of his sanity begins attacking Digger with everything he's got until his punches no longer affect Digger as Boston begins fading away...His mission failed. In the epilouge it's revealed that Boston is stuck in a void of nothing but complete darkness, a light grows brighter as Boston awakes and rushes towards it. As he reaches the light a voice speaks to him, telling him that dead isn't really dead (similar to what The Entity told Boston when he tried to revive . A figure emerges from the light and is revealed to be Dawn, they embrace as the page fades into white.

 These are pretty much just some random ideas and I'm pretty sure that Geoff has got an awsome yet saddening ending for Brightest Day.

"