I remember a topic very similar to this one not long ago, ill try to find it. in the meantime, please use the search function.
If you cannot find it even though you know it existed, how do you know I didn't already use the search function? I don't mind people pointing me at existing threads and tsking me for missing a prior thread, but just randomly dropping into someone's thread and saying "use the search function" isn't exactly productive.
Nor would it be on topic for us to discuss this further in the thread if you do not also provide a link to the prior discussion.
If you meant this thread: http://www.bay12forums.com/smf/index.php?topic=113112.msg3811298#msg3811298
I did not participate in that thread because the original post was aiming at some sort of dwarven personality rewrite, not dwarves moving elsewhere. Emmigration was noted in the thread, but was not the whole purpose of the thread.
This HAS been discussed before. I know, I participated.
Anyways, let's use this thread since it's here.
My other typical comment: Planned.
Anyways, the biggest problems would be figuring put when to leave (I'm unhappy! I'll just wander out through these evil wilds...), and how to leave (I'll march out through the caverns!). Leaving with caravans makes sense under almost all circumstances, but safe lands or places near the Mountainhomes should also have dwarves trekking put alone.