Is it permissible to return to the original high-wage area with closed mosques, except for one distant mosque, given the stable security situation there, even though the area from which one migrated was half Sunni and half Shia?

There is no harm in returning to one's dwelling, even if it leads to missing congregational prayer, due to the mosque's distance or lack of safety. There is no evidence that obligates moving or staying away from one's home for the sake of praying in the mosque. Prayer in the mosque is only obligatory if the call (adhan) is heard and it is possible to go safely.