Tudo bem, eu tentei outra coisa, O que eu fiz foi, Copiei o backup da pasta / etc / mysql da antiga versão, renomeiei my.cnf para mysql.cnf e executei
root@thegamingcorner:~# dpkg --configure -a
Setting up mysql-server-5.6 (5.6.25-0ubuntu0.15.04.1) ...
update-alternatives: warning: alternative /etc/mysql/my.cnf.fallback (part of link group my.cnf) doesn't exist; removing from list of alternatives
update-alternatives: warning: forcing reinstallation of alternative /etc/mysql/mysql.cnf because link group my.cnf is broken
2015-09-28 10:40:02 0 [Warning] Using unique option prefix key_buffer instead of key_buffer_size is deprecated and will be removed in a future release. Please use the full name instead.
2015-09-28 10:40:02 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2015-09-28 10:40:02 0 [Note] /usr/sbin/mysqld (mysqld 5.6.25-0ubuntu0.15.04.1) starting as process 9669 ...
Setting up mysql-server (5.6.25-0ubuntu0.15.04.1) ...
Depois disso, consegui limpar e reinstalar o mysql com sucesso.