What if Stalin doesn't order it? What if some hot head in the KGB decides to carry out an assassination attempt on Tito in the hope of impressing Stalin and being promoted? I know that Stalin kept a tight control over his security service, but semi-official attempt might still be made. In fact an incompetent, unofficial assassination attempt might be even worse. Its more likely to fail and be traced back to Russia. Russia will, truthfully say that they know nothing but I doubt either Tito or the west will believe them. This might scare Tito enough that he moves closer to the west for safety. While Stalin might have allowed Tito to stay neutral he won't allow them to ally with the west. Paranoid he panics and invades.Tito's purge of Stalin aligned communists was rather effective. Also, would you care to note assassinations conducted by the Stalin led Soviet government where the Soviet government did not physically possess by incarceration the victim? It isn't a common political tactic at all between states.
yours,
Sam R.