Delete user is now possible at Admin Panel. But you should remove user first from all boards,

because otherwise there could be bug of empty avatars at boards, that need to be removed manually
from database.

Thanks to xet7 !

Fixes #3956

client/components/settings/peopleBody.jade

@@ -571,10 +571,14 @@ template(name="settingsUserPopup")
       a.impersonate-user
         i.fa.fa-user
         | {{_ 'impersonate-user'}}
+    br
     hr
     li
       form
         label.hide.userId(type="text" value=user._id)
+        label
+          | {{_ 'delete-user-confirm-popup' }}
+        br
         div.buttonsContainer
           input#deleteButton.card-details-red.right.wide(type="button" value="{{_ 'delete'}}")
   // Delete is enabled, but there is still bug of leaving empty user avatars

client/components/settings/peopleBody.js

@@ -979,10 +979,13 @@ Template.settingsUserPopup.events({
   },
   'click #deleteButton'(event) {
     event.preventDefault();
+    Users.remove(this.userId);
     /*
-    // Delete is not enabled yet, because it does leave empty user avatars
-    // to boards: boards members, card members and assignees have
-    // empty users. See:
+    // Delete user is enabled, but you should remove user from all boards
+    // before deleting user, because there is possibility of leaving empty user avatars
+    // to boards. You can remove non-existing user ids manually from database,
+    // if that happens.
+    //. See:
     // - wekan/client/components/settings/peopleBody.jade deleteButton
     // - wekan/client/components/settings/peopleBody.js deleteButton
     // - wekan/client/components/sidebar/sidebar.js Popup.afterConfirm('removeMember'
@@ -990,7 +993,7 @@ Template.settingsUserPopup.events({
     //   but that should be used to remove user from all boards similarly
     // - wekan/models/users.js Delete is not enabled
     //
-    //Users.remove(this.userId);
+    //
     */
     Popup.close();
   },