Richard Baxter struggled with the question of church division way back in 1670. He worked as hard as anyone to maintain the unity of the church but asked that people would be realistic in their expectation of it/ He took the view that the church here is a hospital of diseased souls of whom none are perfectly healed in this life. He recognized that people would be at different levels of spiritual maturity and have different needs according to their age. He warned against the sins of pride, back-biting, and judgmentalism and the dangers of being manipulated by those who were more passionate about some things than others. And then he drew attention to the crucial issue. Where separation is considered the right way forward in practice, we must continue to recognise each other as part of the body of Christ and never disfellowship one another. (pg. 150 Discerning the Spirit of the Age by Derek Tidball)
This only applies if the separation is not due to some of the group adopting and following false teaching.