I think that Roth underestimated Michael and really expected/hoped that Michael would believe that the Rosatos acted on their own. Roth's way was deception and deflection. The Corleones kill Moe. Roth does nothing. The Corleones push Roth affiliates out of Vegas. Roth sends Johnny Ola to give his blessings.
When an attack does come it's something that only could have happened with the help of a traitor and something for which Roth had already provided a ready made scapegoat-Pentangeli. But it wasn't direct from Roth. Not his style.
I think Roth would have survived as long as he did because he might have been a "let's you and him fight" sort of boss.
"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.
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