Keep in mind that the assassination attempt was set up to frame Frank Pentangeli. There's no reason to believe that Neri, Rocco, etc. would ever have linked Roth to it. And Roth would have been smart enough to remain safely in the background while the dust settled.

I would imagine that Roth's hope was that Pentangeli would be blamed and eliminated. That would give the Rosato Brothers the opening to take over NY operations.

As for Nevada, it depends on the reactions of Neri, Rocco, and Tom. Roth would probably have Ola get a feel for how they were leaning under the guise of continuing the business they were already working on. We are led to believe that they probably would have fallen in line because they are "businessmen." If they didn't, I think Roth would have worked behind the scenes to squeeze their casino business, weakening Nevada while the Rosatos got strong enough in NY to control the entire Family.