NBC released a list of there TV hows that had gotten renewed for another season, and Constantine was not there. The show has an awful timeslot and has recently taken a ratings drop recently. So the show has basically been hanging on by it's last limb for a while now, so if Constantine was canceled it would not be surprising.
Constantine does though have a fanbase, who have been tweeting out #saveconstantine sort of this show's version of Community's #sixseasonsandamovie. But it seems that wishing really hard, surprisingly is not enough for networks to realize that if you put a great show in a shit timeslot, you are probably going to make the mistake of cancelling the show.
Although we do now how well NBC does at keeping their best shows going... Community.... Parks and Rec... Freaks and Geeks... Star Trek... I could go on about why so many tv networks piss me off (damn you to hell Fox Firefly had limitless potential) but that would make this a very angry article and no one wants that!
But still there is hope, two episodes left to air and no official cancellation. My best guess is that NBC is waiting to see what happens with the ratings of the last two episodes of season 1... And possibly the whole show. So, I say renew it and god damn it give it a better timeslot than FRIDAY NIGHT! Should Constantine be renewed? Should it connect to the Arrow/Flash-verse? Why do NBC and Fox both cancel shows with great possibility (because they suck)