Who would you rather have in the party: Alessio or Bagheera? If you'd rather have Bagheera, then perhaps he could be brought back.
My thought would be that the party would go on some kind of side quest to plead with the nature spirits to release Bagheera to return to flesh. This quest would be fraught with peril of course, what quest isn't? Think of a place where Divine powers do not work, or are severely limited. And of course, there would be a sacrifice required (we'll assume Alessio would do, but perhaps some other offering besides a soul would do).
Would you as a player be willing to derail the main quest long enough to do that? Would James as DM want to come up with such a side quest (1-2 sessions max I'd hope). Would your characters want to do it?
And what are the ramifications for the group if we sacrifice current members and/or treasure to return an old companion?
… just thinkin'… ;)