Obviously, there is a means by which the train receives requests for help. And that means must involve receiving messages while the train is in the Void, so it's clearly a trans-Void kind of transmission. I would SO like to know how that works!

And as for the Voidtrecker Express trusting us, maybe we'll get lucky and the train will tell us what that thing is, that something major that would convince it that we are trustworthy.