Strange can't help but laugh a little as Childermass remarks that really, dude, don't do it. But, as Childermass so lovingly informed him earlier, both of them are aware that Jonathan Strange has a looooong list of terrible qualities. That disappointment thing is happening and at least both of them are aware of it.

"I agree. England would be lesser without you, John Childermass. Do try to come back in one piece."