Theresa – Clearly articulating the vision throughout the life of the missionary, and “ritualizing” it into the developmental milestones (such as a local church dedication service) creates an awareness in all the parts (the church, supporters, family, mission) of the multiple possible futures of this mission life. (One mission I know of has this sentence in their dedicatory service of their missionaries - “I will accept the potential dangers associated with ministry among the least reached, which may include suffering and martyrdom.”)
Clearer articulation will address the difference in perception and expectation of what missions will be like. There is a sense that the mission needs to make it right when bad things happen, or that the mission did something wrong to allow something bad to happen, and therefore, the mission bears the blame. Member Care that begins with “We will keep you safe…” is in for big trouble. Member Care that begins with “we will help you understand and cope when bad things happen…” starts from a more realistic perspective. I see so many hurting missionaries that feel betrayed by their mission because they perceive the mission to be the cause of their pain, when it may not have been necessarily so.
Will missions make mistakes? Absolutely! They are unavoidable. However, utilizing your idea of integrating the vision of the mission in foundational mission documents may keep everyone focused on the big picture.
Disclaimer: not official legal or psychological advice or opinion