He pauses at the doorway, standing next to her, long enough to say,

"If it gets bad enough, Milliways will throw a Door at us and we'll find someone who is qualified."

He makes his tone reassuring, though not patronizingly so. Just because it's not going to be a difficult escape doesn't mean they have the luxury of her being distracted. He wants her focused, and the best way to get that is to minimize her anxiety.