I don’t think they HAD to leave by that gate, they find an exit into some foothills. *point of clarification, I’m maybe half way into Oathbringer so I’m sure I haven’t read every reference to the gates being locked/why they’re locked.
Every gate being locked doesn’t make sense. If there’s no Radients to operate them there’s no reason to lock them and if they thought there would be Radients left this seems like a minor inconvenience. I guess I’ll just have to wait and see if reasons are forthcoming.