I will have to search for that passage but as I remember it is fleshed out in the novel that if Michael had died as if the attempt was to kill Don Tommasino and even Vito wouldn't have suspected the bomb was actually meant for Michael

However Fabrizio seriously think, he wouldn't be the prime suspect in planting the car bomb
The lure of US, temptation and greed blinded him to the obvious I reckon dead man either way