Some will, some won't, some are already here (how quaint the idea of monogamy - very few actually practice it outside of marriage, and marriage does not calm the urges either).
Polygamy won't happen per se, classical marriage will just slowly disappear which allows for the same result. Given the disgusting state of marriage/divorce law and practice, I have a hard time faulting people who write their own marriage/relationship contracts while staying outside the template provided by the State. As a side effect, this allows far more liberty with respect to alternative marriage structures for those that desire them.