Hi Javi,
You can detect nodes being delted/inserted to the Model by means of the NodeCollectionChanged event.
AddHandler Diagram1.Model.EventSink.NodeCollectionChanged, AddressOf EventSink_NodeCollectionChanged
Private Sub EventSink_NodeCollectionChanged(ByVal evtArgs As CollectionExEventArgs)
End Sub
You can detect the supr(Delete) key from the diagram's keydown event if needed.
Please download the sample explaining it from the link below.
http://help.syncfusion.com/support/Diagram.Windows/Incidents/NodeDelete/Diagram_WF_Delete.zipRegards,
Dinesh