I am displaying the message via Script Task, in SSDT, using the standard pop up window code,
string message = "Task is completed.";
string caption = "ATTENTION";
DialogResult button = MessageBox.Show(message, caption, MessageBoxButtons.OK, MessageBoxIcon.Information);
Dts.TaskResult = (int)ScriptResults.Success;
This is occurs at the end of workflow, which is occurs successfully.
The million dollar question is, how would I get Excel to know when the .dtsx package has completed?
So far, I haven't been able to have Excel communicate with SSDT, other than kicking off a the .dtsx file.