I was driving back and forth at the top of the map (gas station/mod shop) looking for a tow truck, when I see one driving down the road. I shoot the driver in the head and the truck crashes in someone's driveway. I now have cops so I run across the street and hide behind a wall. When the cops leave, the truck parked 30 feet across the street has despawned. Is there a certain radius, where If you're not looking at it, cars will just disappear? If so, what is this radius?
This has nothing to do with a radius or timer. As soon as an object is not inside the "camera", it will be garbage collected by the engine and deleted at the next dump. I've literally had vehicles de-spawn just seconds after I've exited it; Get out close to a wall, fall over making the camera spin, turn around and the vehicle was gone (4-6 seconds).
I guess they didn't consider this for consoles with limited system resources, but for PC the garbage collection shouldn't be as harsh as it is. It's game breaking in my opinion.
Not a radius from my experience but rather a "if you don't look at it for 50 mins its gone" type of system. This is very annoying. Crashed expensive modified Sultan RS that I took for rally. Went less than 50 meters away. I turn around, no car. This is also annoying if I'm in a situation like the one you described, where you want that vehicle but it despawns.