Well, leaving the becoming Grey Wardens alone, the main point is: who has the chance of going through their origins' story without Duncan's help?
Human Noble: He was at the secret passage when Duncan showed up, along with his own personal mabari hound. I trust that he could have gotten away from there without many problems. As to why he would head to Ostagar? That's where his brother and most importantly the king is. His whole family has just been murdered, he would demand justice.
Human/Elven Circle Mage: If acting along with Irving's plans, the mage can get away relatively with a light sentence, even to Gregoir's insisting. He can still be imprisoned for a time, but I'd say in the tower, not in the mages' prison of the templars.
City Elf: Without Duncan, the elf would die or be kept in the Bann's dungeon prisoner, like Soris if the warden is not a city elf who took the blame on himself.
Dalish Elf: Dead, dead, dead. Without Duncan, death is all that awaits the Dalish Elf origins character. Becoming a grey warden is his only chance to survive, as ironic as that can be.
Dwarven Noble: His sentence has been exile in the deeproads, that is a 99% damnation to either insanity or death... 99% because we've seen in-game people who have survived in them long enough. Would be a shocker ending for that quest. Bhelen and Harrowmont fight and fight, and: ta'da. The Warden comes back with the dwarven noble in tow.
Dwarven Commoner: His sentence was between death at the ends of his boss's colleague or exile from Orzammar's laws. If I were him, I would gladly choose exile. Gorim is seen in-game married and a merchant in Denerim after the exile, after all. That spells survival for me.
Now, follow me here. We see in the dwarven noble origin that Ducan has not travelled to Orzammar alone, but he has travelled there with the other grey wardens. That probably means that he reputes that visit most important. So, I think it can go like this.
Duncan goes to Orzammar, and like in the Dwarven Noble Origins, he saves him, or he can be found during the deep roads quest, while the dwarven commoner gets exiled, to be found again later on in the game, somewhere else, or he can be removed entirely.
Now, both the Circle Tower and the Brecilian forests are on the way back to Ostagar from Orzammar. If he was trying to recruit allies, it would make sense for Duncan to stop at the tower on the way back. There he can also use the rite of conscription to save the circle mage (personally, I didn't tell Irvin shit about the plan. So, that means that maximum penance was in order).
Also to tie the mage character with the Denerim situation, makes sense making him an elven from the alienage, maybe Shianni's and Soris' cousin, having received notice before his Harrowing of Soris' wedding (or are circle mages prohibited from doing that? Keeping in touch with their families). The chantry has no control over the dalish, so it makes sense for an elven mage to come from the alienage.
About the dalish, Duncan seemed to have made a detour just to warn them to leave the southern part of the woods, since they could be soon overrun with darkspawn. Again, it's on the way. That makes him able to collect the tainted dalish elf to join.
So, the idea sounds better like this. Duncan goes to the Circle Tower and comes back with an elven mage from the alienage. On the way there, he also picks up the dalish. In the meanwhile, the human noble has survived and has arrived to the camp, requesting justice from king Cailan. There, they meet. Regarding the human noble, Duncan is choosing their guard captain more like a second choice to the Cousland, so he may or may not ask him to go through the joining as well. He would have no reason to do so, though... Well, that can be worked in, actually. With the quest of the keneel master.
Let's say that on the way there, the dog got tainted with darkspawn blood. Being his last friend at the moment, the noble asks to follow the warden's candidates to find the flowers to cure him. They say yes, they say no, he goes in, and he gets tainted as well, cue him being in the same boat as the dalish, and as such, having to go through the joining to survive.
How does it sound so far?
Human Noble: He was at the secret passage when Duncan showed up, along with his own personal mabari hound. I trust that he could have gotten away from there without many problems. As to why he would head to Ostagar? That's where his brother and most importantly the king is. His whole family has just been murdered, he would demand justice.
Human/Elven Circle Mage: If acting along with Irving's plans, the mage can get away relatively with a light sentence, even to Gregoir's insisting. He can still be imprisoned for a time, but I'd say in the tower, not in the mages' prison of the templars.
City Elf: Without Duncan, the elf would die or be kept in the Bann's dungeon prisoner, like Soris if the warden is not a city elf who took the blame on himself.
Dalish Elf: Dead, dead, dead. Without Duncan, death is all that awaits the Dalish Elf origins character. Becoming a grey warden is his only chance to survive, as ironic as that can be.
Dwarven Noble: His sentence has been exile in the deeproads, that is a 99% damnation to either insanity or death... 99% because we've seen in-game people who have survived in them long enough. Would be a shocker ending for that quest. Bhelen and Harrowmont fight and fight, and: ta'da. The Warden comes back with the dwarven noble in tow.
Dwarven Commoner: His sentence was between death at the ends of his boss's colleague or exile from Orzammar's laws. If I were him, I would gladly choose exile. Gorim is seen in-game married and a merchant in Denerim after the exile, after all. That spells survival for me.
Now, follow me here. We see in the dwarven noble origin that Ducan has not travelled to Orzammar alone, but he has travelled there with the other grey wardens. That probably means that he reputes that visit most important. So, I think it can go like this.
Duncan goes to Orzammar, and like in the Dwarven Noble Origins, he saves him, or he can be found during the deep roads quest, while the dwarven commoner gets exiled, to be found again later on in the game, somewhere else, or he can be removed entirely.
Now, both the Circle Tower and the Brecilian forests are on the way back to Ostagar from Orzammar. If he was trying to recruit allies, it would make sense for Duncan to stop at the tower on the way back. There he can also use the rite of conscription to save the circle mage (personally, I didn't tell Irvin shit about the plan. So, that means that maximum penance was in order).
Also to tie the mage character with the Denerim situation, makes sense making him an elven from the alienage, maybe Shianni's and Soris' cousin, having received notice before his Harrowing of Soris' wedding (or are circle mages prohibited from doing that? Keeping in touch with their families). The chantry has no control over the dalish, so it makes sense for an elven mage to come from the alienage.
About the dalish, Duncan seemed to have made a detour just to warn them to leave the southern part of the woods, since they could be soon overrun with darkspawn. Again, it's on the way. That makes him able to collect the tainted dalish elf to join.
So, the idea sounds better like this. Duncan goes to the Circle Tower and comes back with an elven mage from the alienage. On the way there, he also picks up the dalish. In the meanwhile, the human noble has survived and has arrived to the camp, requesting justice from king Cailan. There, they meet. Regarding the human noble, Duncan is choosing their guard captain more like a second choice to the Cousland, so he may or may not ask him to go through the joining as well. He would have no reason to do so, though... Well, that can be worked in, actually. With the quest of the keneel master.
Let's say that on the way there, the dog got tainted with darkspawn blood. Being his last friend at the moment, the noble asks to follow the warden's candidates to find the flowers to cure him. They say yes, they say no, he goes in, and he gets tainted as well, cue him being in the same boat as the dalish, and as such, having to go through the joining to survive.
How does it sound so far?