Helicopter won't extract in "Firing From Vehicles"-showcase.

[OMAC 254]

There could have been another (optional?) task in the mission to clear out all enemies from area, or, even better, an optional task to search town for intel which would complete once you found secret room. Such a task would have given a reason to search village for secret room. As it is now, all your squadmates (if in SP) must wait in chopper while you search town.

[Wiki 1558]

Well, it seems I've found that secret room, wasn't aware at all it was secret.