If no one, not even Michael's own brother, Fredo, gets a pass for betrayal, it is a given that Fabrizio, Willie Cicci got whacked as well

But Michael wasn't a 'Don' by Fredo's murder He was a legitimate businessman!

Whilst Fredo's betrayal could have wiped out the entire Michael Corleone family, they survived
Michael and Kay were still alive

As a matter of interest, the above perhaps is not dissimilar to Vito telling Bonasera "That [murder of the two boys] is not justice your daughter is still alive"

However Vito never even envisaged the fury, resentment, hatred etc. that Fredo would harbour towards Michael for Fredo being stepped over in favour of his kid brother, Don Michael, so much so, Fredo arguably helped set up Michael's murder for Don Fredo [albeit Roth's puppet]

I also believe Vito [Michael too] could have nurtured Fredo by giving Fredo at least a glorified face saving role in the family to show that Fredo is valued in his own right, Michael's right hand man, Consigliere or something