Hi Jereth,
Thanks for bringing in the biblical theology perspective. The apostle Paul seems to allude to the OT law when he commands the Corinthians, 'Expel the wicked man from among you'. God's people are to be set apart, consecrated to Him. Let's continue to explore the full biblical picture further.
I thought I'd bring in the conversation stopper: The Constitution of the Anglican Church of Australia

Here are the fundamental declarations followed by a snippet outlining the terms of fellowship with the Church of England.
CHAPTER I. - FUNDAMENTAL DECLARATIONS
1. The Anglican Church of Australia, being a part of the One Holy Catholic and
Apostolic Church of Christ, holds the Christian Faith as professed by the Church of
Christ from primitive times and in particular as set forth in the creeds known as the
Nicene Creed and the Apostles' Creed.
2. This Church receives all the canonical scriptures of the Old and New Testaments as
being the ultimate rule and standard of faith given by inspiration of God and
containing all things necessary for salvation.
3. This Church will ever obey the commands of Christ, teach His doctrine, administer His
sacraments of Holy Baptism and Holy Communion, follow and uphold His discipline
and preserve the three orders of bishops, priests and deacons in the sacred ministry.
This Church will remain and be in communion with the Church of England in England
and with churches in communion therewith so long as communion is consistent with
the Fundamental Declarations contained in this Constitution. (Chpt 2.6)
This is very significant. The official position of the church is that it will remain in fellowship with CofE and other related churches provided that doing so would not be a) inconsistent with the creeds b) an implicit denial of the authority of Scripture, and c) would not compromise the church's capacity to carry out the great commission
in its fullness.
The constitution clearly does not draw up the bounds of communion in the same fashion that we tend to. It doesn't opt for the pragmatic approach which is prepared to compromise on commands and teachings of Jesus that aren't, in human judgment, necessary for salvation. It doesn't simply try to preserve a lowest common denominator of doctrine which is absolutely essential, while keeping quiet about everything else.
Neither does it say that the Australian Anglican Church will remain in fellowhip with the Church of England as long as CofE comprises a number of 'real genuine Christians'. It doesn't make conversion the ground of visible communion (I say visible because conversion
is the basis of invisible communion).
Rather, we're given the idea that communion is contingent upon the church's ability to uphold orthodoxy and fulfill the great commission. If communion with another church definitely starts to encroach on our ability to 'obey the commands of Christ, teach His doctrine, administer His sacraments of Holy Baptism and Holy Communion, follow and uphold His discipline and preserve the three orders of bishops, priests and deacons in the sacred ministry', then, constitutionally, we'd be obliged to separate.
So, as far as the constitution goes the ultimate question is: does remaining in communion prevent us from obeying any portion of God's word? If the answer is yes, then we need to separate. If the answer is no, then we ought to remain in fellowship.
In Christ,
Jordan
P.S. I concede that the three orders are not commanded in scripture and therefore ought not to be included on the same level as the preceding injunctions (though unfortunately they have been).