I've done it both ways...filled and unfilled. I like using black epoxy to fill cracks, but I usually don't fill large voids, as I think it looks weird. On that piece, I'd probably leave it as-is.
Filled:
Unfilled:
On a related note, just because a piece of wood has a bark inclusion or natural void doesn't guarantee it'll look good. I've made a lot of pieces with natural "features" that look like they're missing something. Look at the piece from an aesthetic standpoint, not just from a "this is challenging" point of view.

Here's an example of one that didn't look as good as I thought it would:
From this angle it looks kinda cool:
But like this, it looks "off", in my opinion: