Ok, forget about exile. What about the idea of permanent house arrest? Fredo is never allowed to leave the compound again. Period. He's stripped of all authority and responsibility and no one even talks to him. He has no access to the outside world. in short he becomes the mafioso in the Iron Mask. Would that have satisifed fears about possible future threats or is only death good enough?

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.