Right now if user removes an account all their reviews are removed too. See http://git.io/T180bQ.
During discussions on IRC we came up with two options that should be offered to user during the account removal process:
1. Permanently remove account and reviews that are associated with it.
2. Remove user account and but leave their reviews.
For more info see IRC discussion logs: http://chatlogs.musicbrainz.org/musicbrainz-devel/2014/2014-06/2014-06-02.html#T19-39-55-873369