Sorry, the question about priest unattached to a parish is not about those who leave Orthodoxy, but like in Catholicism that certain priests function more administratively than an actual parish pastor. But I guess these priests who do not have a regular parish ministry are attached anyway to the Cathedral under the bishop (speaking about the CC here). But then there are bishops without territories, like those on the Roman Curia (or maybe technically because they are in the Papal Office, their territory is the entire CC, not sure about that). But anyway, that was my question if any priest or bishop can be regular priests and bishop in Orthodoxy but unattached to such role or office.
Well, a Church is a diocese, not a parish. Every bishop is the bishop of a diocese (or an auxiliary bishop assisting the bishop of the diocese, but still attached to that one diocese). The bishop has a council of presbyters with him. In the early Church those presbyters served with him in the one community of the Cathedral church, which was equivalent to the diocese. In time, the dioceses became subdivided into parishes, and the bishop delegated presbyters to be heads of those Eucharistic communities as his representative. But those communities are not independent Churches, they are an extension of the bishop's Eucharist. So today you can have a presbyter as a head of a Eucharistic community, in obedience to the bishop of the diocese, you can have a presbyters assisting the senior presbyter, or you can have a presbyter attached to the Cathedral Church, assisting the bishop there, which could have a more administrative role such as teaching, but would still be assigned to an altar. Now, you can also have a presbyter in a monastery, but that's really not much different than a presbyter in a parish Church. Ideally, presbyters should not be moved from the altar and community to which they were ordained except in extreme circumstances, though today it happens frequently. So you see, even priests whose primary role is something like teaching are still in a position in the Community, which is properly understood as the diocese as the whole, not one parish within it. Ideally, a diocese should function as one Church under one father, not as separate Churches... but that doesn't always happen. A priest should be an elder in a community... so really someone shouldn't be made a priest just because they're a seminary professor without being in a true role of fatherly care in the diocese... though I'm not saying the ideal is always followed.
Now, a bishop without a diocese is a contradiction in terms. A bishop is the overseer (chief servant) of a diocese. That's simply what a bishop is. Does that mean we always follow this today? No, the EO have "titular bishops", who are given the tital of a defunct see they never set foot it in and then assigned some service. This is really nothing but a lie. The Copts have developed the notion of "general bishops" who don't have a geographic see, but a service general to the "Coptic Church". This is really the heresy of Phyletism, believing the Coptic Church is a Church separate from the other Orthodox "Churches", as a "part" of the One Holy Catholic Church. This is a serious error, a deviation from sound Orthodox Ecclesiology. In fact, it seems to be occurring because of an uncritical assumption of Roman Catholic ecclesiology, and a profound ignorance of Orthodox ecclesiology.
But the fact that we are messing up and organizing wrongly today because of ignorances does not change the fact of what proper Orthodox ecclesiology is. Roman Catholics say that the Orthodox say they don't believe in ordination as an indelible mark on the soul, but the fact that we don't reordain returning lapsed priests shows that we really do believe in "once ordained always ordained" like the Catholics, we just don't want to admit it because we want to be different... No, our understanding is different, it explains our practise of not reordaining without having to accept the scholastic idea of an indelible mark on the soul as the underlying reason. The fact that we're making mistakes in our organizing and not reflecting proper ecclesiology does not change the fact that it is true.