following a vehicle, that vehicle crosses into the left lane running a vehicle off the road, they lose control cross over and hit our vehicle head on.

This sounds like a question of fact as to whether Vehicle 2 is liable and a potential uninsured motorist claim. Going on the premise that Vehicle 1 is long gone, then the issue is whether the driver Vehicle 2 negligently failed to control his/her vehicle.  From what you have described, you are likely looking at needing to file a lawsuit and letting a Jury decide.  Hopefully there are photos of the property damge caused by the alleged collision between Vehicle 1 & 2.  The reason for being able to prove the initial collision is that if you have uninsured motorist coverage, then your policy may require objective proof of the collision to qualify the accident as one involving an uninsured motorist.  Hit & run is considered an uninsured motorist event. IMO, you are looking at litigation to collect anything substantial, and that is only if the Jury buys your version of the accident.