My two cents worth!

Tom and Fredo, sentiments aside....

If Michael had died, nobody figures out who was behind the murder plot, nobody even suspects Fredo and he gets away with his betrayal

If Tom somehow found out Fredo's role in Michael's death, I can't see him brothering Fredo after knowing what he has done

I reckon Tom might well have taken the legitimate offer, on the earliest flight, out of Tahoe to Las Vegas

Pentangeli runs his family without Michael on his back

Roth picks up the Corleone casino holdings after all the bloodshed