Responses
No she was not bannished. Some sadistic translator translated it wrong. Yuri unexpectedly died before Kail which made Kail suffer a lot a die 1 year later, leading to the empires ruin. Read this :
http://forums.mangafox.me/threads/404883-THE-SUMMARY-AND-THE-TRUTH-ON-BANISH-OF-YUURI!!-Neither-the-son-nor-Kail-have-banned!!
Wait did kail really banish yuri?
It does not seem like he would do that
But how did yuri die and what happen to kail and the rest afterwards?