I believe that the differences that you are pointing out depend on several factors, actually two. The first, of course, is whether the transitional deacon is secular or religious. If he is secular, then the rules of the local diocese apply to him. It may be the case that in many dioceses transitional deacons who do not become priests are in limbo, to use your term. But this is not the case in religious orders of Pontifical Right. In the orders, not the congregations (they are an animal with different stripes), the orders, the monks and friars enter for the purpose of being monks or friars, not for the purpose of Holy Orders. Therefore, whether a transitiional deacon becomes a priest or not does not affect the individual’s status in the order. He will always be either a friar or a monk. In the orders, the friars or the monks exercise whatever ministry they are called to exercise, not by the bishop, but by the major superior or the Abbot.
What happens in the orders is that if for some reason a transitional deacon does not get ordained a priest he simply remains a deacon, but his superior grants him the faculties of any other deacon and assigns hiim as he would any other member of the order. It is obvious that if the superior assigns a cleric (deacon, priest or bishop) to work in a diocesan parish or diocesan ministry, he must give an account to the local bishop. But generally, these agreements are already made between the orders and the Ordinaries, so that the bishops only ask for names when the assignments are made and the faculties are granted. In the rare cases where a bishop does not grant faculties within his diocese, the Abbots, Priors and Guardians of the orders still have canonical authority to grant faculties within their own oratories, chapels, friaries, priories and monasteries and other facilities that are within the jurisdiction of the order.
It is very difficult to say that X happens to every transitional deacon. Because there are variations according to dioceses and between the diocesan clergy and the orders. I can’t speak about what happens in congregations, because I don’t belong to a congregation. Most congregations are either clerical or brothers. This would not be an issue that would come up in a congregation of brothers. How do clerks regular (clerical congregations) such as Jesuits, Salesians, Vicentians and Fathers of Mercy etc deal with this, I have no idea. The rules that govern them are very different from those that govern the religious orders of men. But in the religious orders of men, the ordained ministry is within the call to religoius life. Therefore, it is dealt with very differently than it would be in a diocese.
I can say this about the orders. In the orders the permanent deacon is an exception, not the rule. The rule is the non-clerical brother, then the brother priest. There are very few brother deacons in the orders. Those who are ordained deacons do get ordained priests after one year.
I do know that in the orders, the few men who ask to be permanent deacons go through the same formation as everyone else: 6, 4 and 4, between mystical theology for religious life, pre-theology and divinity. There is no difference in the education or the formation program between the permanent deacon and the priest in an order, unless the major superior makes a concession. But these are exceptions, not the rule.
We conclude again with the same point, the rules are not hard and fast. They are rather fluid depending on whether you belong to a diocese, order or congregation. Even if you belong to a diocese, each diocese is a world unto itself, as long as they comply with canon law. Canon law is deliberately broad on some of these subjects. The 1983 code allows the dioceses some flexibility and at the same time tried very hard not to create difficult situations for the old orders that have traditions that go back over 1,000 years.
Fraternally,
Br. JR, OSF