System.Windows.Forms.Integration.ElementHost el_1 = new System.Windows.Forms.Integration.ElementHost();
System.Windows.Forms.Integration.ElementHost el_2 = new System.Windows.Forms.Integration.ElementHost();
System.Windows.Controls.ComboBox comboBox1 = new System.Windows.Controls.ComboBox();
el_1.Child = comboBox1;
 
//Убираем связь между el_1 и comboBox1, после подключаем comboBox1 к el_2
el_1.Child = null;
el_2.Child = comboBox1;

System.Windows.Forms.Integration.ElementHost el_1 = new System.Windows.Forms.Integration.ElementHost();
System.Windows.Forms.Integration.ElementHost el_2 = new System.Windows.Forms.Integration.ElementHost();
System.Windows.Controls.ComboBox comboBox1 = new System.Windows.Controls.ComboBox();
el_1.Child = comboBox1;
 
el_1.Dispose();
 
//el_1 удаляется, но comboBox1.Parent по прежнему привязан
if(comboBox1.Parent == null) el_2.Child = comboBox1;

        protected override void Dispose(bool disposing)
        {
            this.Child = null;
            base.Dispose(disposing);
        }