No Father that I know of taught that "we can't where the Church is not." The Fathers very often defined the boundaries of the Church.
However, we know that the Holy Spirit is everywhere, and in that sense grace is everywhere; some coin this "charismatic grace" although some people do not like the distinction between "charismatic" and "sacramental" grace (although I think it is a natural distinction; nothing could be alive without grace, but we know that for instance the mysteries of heretics are not grace-bearing, so there must be a distinction).
No salvation outside the Church is a normative statement, but Christ can save whom he wills. We know that Christ is just, and it would not be just if say, you were condemned to hell just because you lived in N America before 1492 (or actually whenever the first Orthodox came here!)
While it is highly unlikely that those who are not baptized can be saved, at the same time, given that charismatic grace is everywhere, and given that Christ can save whom he wills, perhaps the people who truly follow him although in ignorance who have not had a chance to encounter the visible Church are given a chance to accept it through the truth written on their conscience. This would of course be an exception, an economy, which does not do away with the standard. If through charismatic grace someone is somehow grafted in to Christ, it is still not sacramental grace, and they still cannot attain deification in this life.