Im about to replace the spring seat and strut mount because mine has failed. Is it necessary to replace the bump stop too? Do those go bad?

 

I would say they go bad in the sense that they degrade and possibly crack. It's not structural or under constant force like the strut mount or spring seat. I did not replace mine when I replaced the strut/seat/mount. If I wasn't so cheap, I would have replaced it and the boot also.

 

If its coming apart and no longer able to stay in its mount, replace it.