A little more detail would be helpful, like what is this facility, what makes you say it has a magnetic field, how are you losing control (what exactly happens)?
We do not recommend to fly in the place where there is a chance of strong magnetic interference, such as magnetite, parking structures, and steel reinforcements underground. May I know what happened to the drone?
If you fly inside a complex with a strong magnetic field you will probably crash, I would definitely avoid that place.. if you decide to try anyway make sure you take a video so we all know the outcome..