Deleting a parent term deletes all menu children

In some cases user add own menu items in taxonomy menu synced menus.

If however those menu items are children of a taxonomy term, deleting the term leads to deletion of all custom children menu items.
Administrators of drupal would expect that the menu items would fall out of the parent and stay on level higher. This is standard Drupal behaviour.

Recursive deletion leads to potential data loss and much manual work to redo...
We should either stop deleting a menu item if custom children are present or we should make them detach to the top level instead of delete.