Fredo sort of vacillates between uselessness and borderline cunning in Pt. 2. Fredo may of had enough money in his pocket to get back to Florida and some stashed in New York where he went to ground. I guess we're to infer at least this much from the fact that Fredo did get out on his own and back to New York.

I think though, given Michael's vindictiveness, that if he thought Rocco was in on the Tahoe assassination attempt that he would of have had him killed sooner once he was safely back home. Also, if Michael really suspected Rocco would he of left the Family in the hands of Tom?