Well that's an issue.
Why did that sieze to shaft? That's the most important question.
What kind of oil were you running? Did you have the right amount? Was it maintained? How long was the motor together? Did you do anything prior to this? Is that oil plate in place behind the basket?
These are all things that need to be taken into account before you rule out part failure. Because swapping parts won't fix it if you don't know what caused it. I work on a few bikes around the neighborhood so these are all thing I would ask. Let us know and maybe we can find out what happened.