Obviously, Ivan betrays Eraser; he just wanted to get rid of a rival.
Ivan tries to play the "father figure" card, claiming he put him in that room to prevent a collapse—never mind the others. Did they really think the rest of the guild wouldn't show up to help Laxus?
Eraser gets one-shotted, even though he has the ability to erase distances; instead, he lets Natsu and Laxus get close.
Anyway, for the final chapter, I have a feeling Ivan will be at the parade, lurking in a corner and having a quick chat with Makarov.