Can an orthodox congregation remain part of that synod? Can an orthodox pastor?
Speaking to that matter is Thesis II of the document “Communion Fellowship” in volume 1 of Essays for the Church by C.F.W. Walther.
A fellowship in which the Word of God is fundamentally falsified, or in which a fundamental falsification of it is tolerated, is not a true orthodox church, but a false, heterodox church or sect.
I’ve read this before, and intend to read the section again when time permits. It serves as an excellent basis for discussion of several different circumstances in present-day Lutheranism.