Have not seen that in a loooong time. This used to happen on the old 89s before they updated the impeller shaft design.
Sorry to say we never had much luck getting the end out of the impeller, of course those were all aluminum units back then. This is why we stopped using loctite and factory torque specs when we put impellers in.
If you can drill the shaft out to a large enough size they do make an "easy out" that large. Find an old drive shaft, chuck it up in a vice, put a lot of heat in the thing and be very gentle trying to spin it out.
What machine is this?