The Jurists have differed as to when Darul Islaam becomes Darul Kufr.
The Shaafi'i school holds the opinion that Darul Islaam never becomes Darul kufr under any circumstance even if the Kaafirs gain the upper hand and drive away the Muslims from it and their (i.e. the kaafir) laws become apparent there.
They base this on the following narration
الإسلام يعلو ولا يعلى عليه
Both Sheikh al-albaani and Ibn Hajar graded the narration as hasan.
The Maaliki and Hanaabilah hold the opinion that Darul Islaam becomes Darul kufr when the laws of the kaafirs become manifest in it.
Kuwaiti Encyclopedia of Fiqh
Volume 20 Page 202