Given that we only do bi annual sim assessments there is only so much that can be covered and while you may get to have a go at a turnback/short pattern circuit you certainly won't get to be practised at it.
If things really are that dire (uncontained fire) then I'll give it a go based on the thought that if I don't I will die anyway. Nothing to lose. Certainly in my company people do often mention a return to reciprical in extremis and have thought through how to achieve this. How you fly the pattern will depend heavily on the weather conditions at the time.
For me its establishing the severity of the situation that is the key and that will then dictate my actions. Has the fire gone out or has the fire wire just burnt through? How do you know ? In the case of the Nimrods the flight deck had the huge advantage of well trained rear end crew on intercom who rehearsed such scenarios so the flow of info was excellant and enabled quick sound decisions to be made by the flight deck. In the commercial world crew are not trained to respond in that way and the flight deck often do not include them in the loop at an early enough stage to make a difference. We can't see the engines/wing/cabin they can so their discription of what is happening could be key.
I fully support a crew flying a turnback or short pattern in extremis but it is a risky mvr that could in itself lead to tragedy so before its initiated its important to establish that its needed.