Yeah, I know that there was no way of getting any message instantly over a thousand miles away to the leadership at Weisshaupt, but you do realise that nothing was really stopping us from asking the Architect to wait until we'd dealt with the mother before hashing out plans to make an alliance?
It wasn't really a "this must be done now" kinda thing like Shepard was faced with in ME3 where he had to choose Ctrl, Alt or Del with a ticking clock, we were already in her lair and aside from some fire support from the towers if we allied with him, he's not involved in helping us take the Mother down?
Not that I disagree with the actual alliance itself, it's what I chose in that situation, but what baffled me was how quickly we just agreed to help him further perpetuate the sentient race of Darkspawn, when that decision could have been easily been made later? Granted, the Architect had a better bargaining position if he forced us to chose then and there, but for all he knew, we could have all died horribly and so that alliance would have ended anyway?
And while it's safe to say that the epilogues are always semi-canon, it did mention that a lot of Wardens are bothered by our decision to ally with him? How did we know that Weisshaupt wouldn't refuse to go along with the plan, even after we gave the Architect our word?
It also makes me wonder how the Inquisition would react to learning of this alliance, considering that it's not that much different really from what Clarel was attempting to do at Adamant? Except that we actually know we're helping a Darkspawn Magister (although we obviously didn't know he was likely one of the original Magisters) in this case, whereas she was tricked into doing so?
(Incidentally, while there aren't phones, the Mage Circles and the Divine apparently have Sending Stones that function in pretty much the same way. Of course, we neither have one, nor likely does Weisshaupt, just pointing out that long-distance communication devices do exist in this universe)
Except the architect only wanted to ally to kill the mother, it's not like the wardens are having dinner with darkspawn. It was a one shot deal before he vanished back into the deep roads... There's no actual alliance, no matter what you did. It's just an agreement not to stick a sword in his face and team up to stop the children.
The warden didn't make actual peace with the darkspawn, he just made a personal choice to trust the architect and push forward. I doubt his return will be entirely peaceful, he appears to be one of the magisters, he just wants a different fate for the darkspawn then he others.
From the wiki on the awakening epilogues:
If he gains the trust of the Warden, the Architect will keep true to his word, freeing the darkspawn from the Old Gods' call and gathering his remaining disciples to follow the rest of their kind back underground. Those Grey Wardens in other nations were appalled to hear of the Architect's continued existence, saying that it guaranteed another Blight, but were unable to track him down despite years of effort. However, darkspawn sightings grow increasingly rare and the dwarves claim that the Deep Roads have never been quieter.
So yeah, he just vanished and kept making talking darkspawn.