If I have the following controller action...
public void DoSomething()
{
}
will the framework actually convert it to this?
It won't "convert" it, but the two would have the same effect as far as the user is concern. A request would be sent, but no response would come back to the client.
Personally, I think you need to send some response back to the client, even if you just write a continue or success directly to the response stream. Even a JSON true, or an empty XML document is better than nothing at all.