So far i have not seen this....
In the novel The Last Flight, the present day wardens of weisshaupt are concerned with the disappearance of the wardens in orlais, meaning that corypheus has not affected the weisshaupt wardens at that point. It is my interpretation that corypheus only controlled the orlesian wardens, not any of the free marcher wardens, anderfels wardens, or the ferelden wardens.
I think the ferelden wardens are exactly where they are supposed to be, still there. We know those in weisshaupt ordered nathaniel into the free marches to investigate the primeval thaig, so he was at least traveling... at the end of TLF we find out that amaranthine has a new warden commander, so our hero is gone... however why wouldnt ogrhen, velanna, and sigrun stay... if you got all their approvals up properly they do stay with the wardens and dont disappear.
And before you go off saying that clarel would have at least reported their stuff to weisshaupt, especially if it involved ending the blights, in TLF we find out that all correspondences have not been returned from the orlesian wardens... this would be someone of corypheus's crew interrupting them, and anything clarel would have sent would be returned with a fake reply.
So i think that the wardens in the other nations were not aware of what was going on, and it didnt seem like the wardens of weisshaupt were ready to launch a full scale investigation into it either, due to the worrying about the mage templar war issues and the civil war issues. The wardens searching for stroud/alistair/loghain in crestwood would be orlesian wardens, and the ferelden wardens would not be aware of their activities within their borders... Now the question is, why didnt stroud/alistair/loghain go to the other wardens? My guess, fear of not being believed, or fear of corruption within their ranks... that is why he asked for an outside source like hawke for help.