Get Notification when .EXE from task manager or in system Stoped.

If you started some process in your code, you can capture the even when it is stopped, but, normally, you would need to handle it in a separate thread. This is not very expensive even if you want to track several external processes requiring a separate tracking thread per process, because most of the time such thread would be in the wait state, wasting no CPU time.

It could looks like this:

using System.Diagnostics;

//...

void SomeThreadStartMethod() {
    Process someExternalProcess = Process.Start("...", "..."); // some parameters
    someExternalProcess.WaitForExit();
    // invoke some event or handle it somehow...
}

If you are not starting your process in your server, you still can get the list of processes, choose one by some criteria and use a references to it to do the same wait. Please see:
http://msdn.microsoft.com/en-us/library/system.diagnostics.process%28v=vs.110%29.aspx[^].

—SA