The drone needs to go down now, period. If that completely bones our ambush I can live with that and we have a minute or two to reset regardless. Remember, we are still between them and their goal and we have the high ground, in that scenario.
My point of the third car is this: if we can remove it from the equation we need to do it because missles can kill you even when they miss. They are in armored vehicles and can ignore splash damage, Marak and Smiley can't, and we chose our ambush site because of the close quarters. I do not think they will abandon their mission if they lose their backup, they might switch up their route, maybe going for the interstate, but I doubt that too, they are making the run they are making because of the relatively low visibility, the interstate is high vis-go gangs, lots of cops, lots of cameras. If I am wrong, again, we still have the high ground and can reset.
So to recap: Kill the drone, do something to disable or disarm or remove the chase car. When the ambush goes down, hopefully shutdown and poplocks on the target, get in and get gone.