Would it not have been simpler, less suspicious, and more practical for the assassins to have finished the job at the scene of the accident?
You can’t with any degree of certainty kill a person in a slow-moving vehicle by putting a truck in front of him. So let’s say that Patton’s broken neck had some other cause there at the scene of the accident.
Are we to assume that the Russians don’t know how to do this properly? So that he’s dead instead of just paralyzed and requiring additional violence later?
Meanwhile he’s alive and might possibly speak?
Not to mention the witnesses at the scene. Very messy situation, very unprofessionally arranged.
Conclusion: assassination not likely.
Ever read the account of Rasputin's assassination(s)?