Roth's wife could have arranged the private boat through the hotel concierge if it was still functioning or Batista's people if they have not deserted them after his resignation
How did Fredo get out? How could anyone find him in all that chaos
I discussed those points in this thread:
http://www.gangsterbb.net/threads/ubbthreads.php?ubb=showflat&Number=472494&Searchpage=1&Main=16944&Words=%2BFredoRoth+%2Bconspiracy&Search=true#Post472494
What was Rocco doing at the Desert Inn? Why did Michael stop over there Tom and Neri were there too
A
guess is: directorial considerations. Logically, Michael would have met all three at his home in Tahoe. But, FFC was planning to make Michael's return to Tahoe into that deeply melancholy scene we saw (his gift to Anthony of the little car abandoned in snow, Kay working at her sewing machine without looking up when he came in, asking Mama if he could lose his family), so FFC "took care of business" by having him meet the Big Three in Vegas before returning home.