I know Bobby said he's avoiding his reaper, but with Bobby I think it may be a case of regular ghost "unfinished business", that wont let him move on, he just sees it differently.
But, the guy's a hunter! He knows the downside of having angry/fustrated spirits around. Bobby's always been strong enough to do the right thing, and once he's satisfied the leviathans are taken care of or w/e, I think he may be able to rest.

Also on a side note, I think the writers, realized they needed a different or roundabout approach to bringing down the superpowerful leviathans so why not bring Bobby back? as a GHOST? :P