This 3 years old question bothered me much more than it should have.
While it was not a certitude, I was pretty certain that guards would leave damaged vehicles. I was also pretty certain that there were no viable non lethal-options, apart from simply avoiding combat, which is mostly doable.
From your mission's objective, the area seems to be the facilities neighboring the open-pit mine in the mission "Awakening".
Let's put this in 3 points:
- Is there a non-lethal option that permanently disables enemies ?
- No. Even punching is lethal.
- What about the tranquilizer (aka "tactical attachment") ?
- Worthless, as it keeps a guard asleep for maybe a minute at best.
- Can we force guards out of vehicle ?
- Yes, by damaging said vehicle in a manner that would be considered inoperable or unsafe.
"Inoperable or unsafe"
Guards leave vehicles that are damaged to the point of being about to explode. In such case, there is a chance that the guard may not leave fast enough and die. This can be done by shooting the vehicle's reservoir or attached jerrycan until it catches fire. That's the unsafe way.
Guards will also leave a vehicle that is damaged in a way that makes it impractical to drive. Considering the limited damage model of available vehicles, this is essentially a matter of missing tyres.
What comes after the theory
I reinstalled the game. Copied my archived saves. Loaded the right level. Made my way to the quarry. Climbed back on a beloved roof spot. And I shot a tyre to make a KPA soldier disembark a vehicle. This last part can be seen in this video:
Which I summarized in this picture:
And as far as punching a guard manning a gun on a jeep, well, what can I say to that...
You have to kill them. Kill them all. No KPA soldier leaves that quarry. Or in other words:
"No, there is not a non-lethal way to disable guards in vehicles".
Played on Delta difficulty, of course.