Yikes. That doesn't look very nice.
On the plus side, that might just end up being removed as you tiller, but you're gonna want to secure it first. I'd go for superglue instead of epoxy on that. Clamp the bow so it's side-up, pour as much superglue as you can into the crack, all the way down, and make sure it's leaking out the other side as well. Then clamp the whole thing up with a few clamps or a long rubber band to maintain pressure. Let it go off, then see what you've got. It needs to sound good - tap the surrounding wood with a fingernail and take note of the sound. Then tap the glued up area and compare. If it sounds like something's moving when you tap it, or its thin and papery sounding, redo all the glue again.
If a large area like that isn't solid it may end up pulling away from the belly as the bow bends. Not good.
Your other option is to just plough through it until you hit solid wood, then make the best bow possible out of what remains.
If you go with option 2, leave the sapwood at the thickness it is already. If you manage to secure it with glue and it feels and looks solid, get that sapwood down to a sensible thickness and carry on!