It's not out of the question but on the face of it (removing knot from handle, buying new brush and removing knot from there too, hoping knot will fit perfectly n new handle) seems like a complete pain in the butt for what is after all a simple boar knot which you can buy in decent handles for bugger all. After a few uses with a new boar brush you won't know the difference.
You'll get pissed off with using a brush that looks it's been hit by a tractor and if that doesn't happen it'll gradually get skankier looking as soap scum builds up in the cracks and then, assuming the cracks go all the way through, it might start smelling funky because it can't dry out properly. You can try and repair it which might retard the above scenarios but it's unlikely you'll be able to do a repair job that will exclude the possibility of water getting in to the base of the knot.
