The Orthodox Church has the grace of the Holy Spirit.
That's all that needs to be said, and all that can be said with any certainty. Legalistic speculation about when a schism truly becomes a schism and when grace departs from a schismatic group, although interesting, is mere speculation.
It certainly would make sense to say that if an Orthodox bishop leaves the Church and joins himself to a schismatic or heretical body, all those under his jurisdiction would not immediately find themselves in the same situation. However, to construct an ecclesiology on assumptions about when and how a particular body loses sacramental grace (and thereby membership in the Body of Christ) is like building a house on sand. It might work on paper, but won't have any basis in reality.
The determination as to whether a group which has gone into schism has apostolic succession and mysteriological grace belongs in the first instance to the bishops of the canonical Church from which it departed into schism or, if it is a schism of a schism, to the originating canonical Church.
It is the bishops of that Church who exercise the powers of binding and loosing.
In many instances Churches will act very leniently with breakaway groups, praying that charity and leniency will bring them back to the Church.
Sometimes the bishops are quite quick in rendering a judgement of deprivation of sacramental grace. The Church of Serbia, for example, declared officially that the sacraments, including Baptism and the Priesthood, of the Free Serbian Orthodox Church were invalid. We therefore had to baptize and chrismate and marry any people coming to us from the Free Serbian Church.
If we read Jonathan Gress' messages on the Forum I think he says that some of the Greek schismatic groups were deprived of sacramental grace very early by a decision of the bishops of the Church of Greece.
There can be only one Church of Christ. As Archpriest Michael Protopopov notes in his small monograph on +Tikhon Pasechnik and the RTOC:
"If one’s actions take a person outside the Church then that person is outside the Church. There is no alternative. There is no shopping list of churches. There is only One, Holy, Catholic and Apostolic Church."http://pages.prodigy.net/frjohnwhiteford/RTOC.htm