People communicate between the mists all the time. We have had trades and sales etc.. Mainly it is small things between one adventurer and another because we cannot facilitate large interactions between different chapters very easily. An example would be an army you created in one land going through the mists to invade another land. It has been done but only on extremely rare cases where all plot teams involved were ok with it and ready for it. We have also had diplomats from other lands come and create treaties with Valdanis so that is possible too.