Unfortunately, that flow is not possible - there are some technical issues with the way NTLM works and this does not allow us to fall back to forms-based after failed NTLM attempt.
That said, I am still trying to understand the use case - are you authenticating users against the same directory backend? Let's just say, for example, that what you were asking above was possible, and you could get to a login page after failed NTLM attempt - what would that user be authenticated against? Once I understand what exactly you are trying to achieve, I can hopefully offer a workable solution.