In the nearest version FlyGrid, it will be possible, here is a code that you can use to determine selectedindex of value in the dropdown list:
[VB.Net]
Private Sub dgParams_NodeCellChange(ByVal sender As Object, ByVal node As NineRays.Windows.Forms.Data.NodeBase, ByVal index As Integer, ByVal value As Object) Handles dgParams.NodeCellChange
    If (index = 0) Then
      'cast FlyGrid as IServiceProvider
      Dim sp As IServiceProvider = CType(Me.dgParams, IServiceProvider)
      ' get a IDropDownListService instance
      Dim idls As NineRays.Windows.Forms.Grids.IDropDownListService = _ 
        sp.GetService(me.dgParams.GetType().Assembly.GetType("NineRays.Windows.Forms.Grids.IDropDownListService"))
      If (Not idls Is Nothing) Then 'if it supported - receive currently selected index
        Dim selectedIndex As Integer = idls.SelectedIndex
        'output to diagnostics console     
        System.Diagnostics.Debug.WriteLine("Selected Index is " + selectedIndex.ToString())
        'here place your code....
      End If
    End If
  End Sub