When you edit a link, e.g. change its end item, there is no appropriate event to handle this situation. The Links.CollectionChanged event is not fired. It would be nice to have a LinkChanged event which will be fired when a link is modified similar to the ItemChanged event for the tasks.

Workaround:
            foreach (GanttViewLinkDataItem link in this.radGanttView1.Links)
            {
                link.PropertyChanged += link_PropertyChanged;
            }

        private void link_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName == "EndItem")
            {
            }
            
        }