I actually like option 2 the most, if they go boom you replace them. I've had very few of my vehicles blow up. I don't think there should be any invulnerable vehicles honestly as that would just lead to carelessness with them.
Just a few years ago that happened to a couple of firetrucks in two different counties in my area actually. The fire they were fighting shifted directions and they couldn't get the trucks out of the way in time.
we had our tanker burn up it was a big grass fire and the driver couldnt see so he hit the left shoulder and thought it was the right so he jerked to the left put it in the ditch and the fire was to close and even though it had 2000 gallons of watter he left it to burn but it didnt expolde i mean come on cars dont explode like they do in the game