I've answered my own question about the "None" state - an event was setting the thread to None where I didn't expect it.
However, my question slightly repositioned is if a Thread is "Stopped" it still seems to exist. Is there someway to make it go away, send it to garbage collection etc? Other part of the original Q - I assume a Stopped thread gets a false from "isAlive" and a Running thread gets a true? -- http://mail.python.org/mailman/listinfo/python-list