Quote "No you don't understand. If you are off the localiser by full scale deflection and presuming the airfield is in a valley or theres high terrain you are therefore outside the normal approach and a go around in this situation could still be dangerous."
"Would you continue in level flight until the MAP or start a climb straight away- after you've had FSD or the signal has failed??"
Let's see:
You are in cloud.
You are flying an ILS in mountainous terrain.
You suddenly notice that you have flown off track to full deflection on the localizer or that the ILS has gone u/s either in the a/c or on the ground.
You have no other means of establishing you position.
What to do??????
Well: How about waking up the co pilot.
Going to an immediate climb at full power
Going to best angle or best rate of climb speed. I recommend best angle.
Turn as required to try to follow the missed approach tracks as best as possible.
Call for radar vectors if available. Don't be shy: declare an emergency! You have one!
Switch on the "Pray like you've never prayed before." light for the pax.
Climb to the MSA.
Your scenario is way outside of normal ops - you are going to hit something unless you do something right now.