Alright, integrity verified and yep, can confirm that the Gamblers still just pull a hard left and leave the area entirely when we reach the LZ.
Otherwise as you said, the mission still plays on and is complete-able.
Already posted in discord but just posting here for PD919's sake - I'm having the same drama. Tried M2 three times, the gunships bugger off after as we approach the LZ every time. No mods etc. Running a steam verify integrity atm, will report back when I get time to try again.