Change the way nuked users' posts are handled. Allow null in the user_id column of posts. Show these posts in the posts stream.

app/assets/javascripts/discourse/models/post.js

@@ -30,6 +30,7 @@ Discourse.Post = Discourse.Model.extend({
   deletedViaTopic: Em.computed.and('firstPost', 'topic.deleted_at'),
   deleted: Em.computed.or('deleted_at', 'deletedViaTopic'),
   notDeleted: Em.computed.not('deleted'),
+  userDeleted: Em.computed.empty('user_id'),
 
   postDeletedBy: function() {
     if (this.get('firstPost')) { return this.get('topic.deleted_by'); }

app/assets/javascripts/discourse/templates/post.js.handlebars

@@ -17,11 +17,18 @@
     {{/if}}
 
     <div class='topic-meta-data span2'>
-      <div {{bindAttr class=":contents byTopicCreator:topic-creator"}}>
-        <a href='{{unbound usernameUrl}}'>{{avatar this imageSize="large"}}</a>
-        <h3 {{bindAttr class="staff new_user"}}><a href='{{unbound usernameUrl}}'>{{breakUp username}}</a></h3>
-        {{#if user_title}}<div class="user-title">{{user_title}}</div>{{/if}}
-      </div>
+      {{#unless userDeleted}}
+        <div {{bindAttr class=":contents byTopicCreator:topic-creator"}}>
+          <a href='{{unbound usernameUrl}}'>{{avatar this imageSize="large"}}</a>
+          <h3 {{bindAttr class="staff new_user"}}><a href='{{unbound usernameUrl}}'>{{breakUp username}}</a></h3>
+          {{#if user_title}}<div class="user-title">{{user_title}}</div>{{/if}}
+        </div>
+      {{else}}
+        <div class="contents">
+          <i class="icon icon-trash deleted-user-avatar"></i>
+          <h3 class="deleted-username">{{i18n user.deleted}}</h3>
+        </div>
+      {{/unless}}
     </div>
 
     <div class='topic-body span14'>