"
When a Polygamist Is Converted What Should He Do About His Marriages?"
The link is an example of the "problem" faced by missionaries in PM contexts, as noted in
my intro post.
If you don't know John Piper, he is probably the most famous and respected living teacher both in evangelical missionary circles
and Reformed/Calvinist circles. Since I operate in both of those circles, he is one of my favorite guys on
most subjects. He's also a brilliant scholar, and Chancellor of the Bethlehem College and Seminary in Minneapolis founded by him and his church during his pastorate, in part because his amazing teaching gift was attracting so much attention from folks who wanted to come and learn more from him. But in the linked post, he really
agonizes to find a Biblical solution to this very practical question, and in the end he acknowledges that a truly satisfying answer is above his pay grade.
From years of listening to Dr. Piper, I have no doubt that if asked how to pastor an American convert currently living in a same sex union he would have no trouble saying that: (1) their "marriage" is no such thing, so to "sever" it is only to sever a non-existent sham, (2) that their sodomy is sin which must be repented of and forsaken, and (3) that they should have no hesitations about a legal and practical "divorce" since their "marriage" was a sinful non-entity in the first place. But he knows that Scriptural treatment of polygyny is very different from its treatment of homosexuality. So he's held back from this error: "
the Church of England in the nineteenth century held a staunch position that polygamists must divorce all but one of their wives in order to join the church." It appears
the Anglicans loosened up on that a bit in 1988.