Okay, Richie is indeed a civilian. He runs a bar in a Mafia neighborhood. He probably pays protection to the Rosato brothers. So, he knows that in such a neighborhood he could be a dead man for any number of reasons even as simple as serving one of the Rosato brothers the wrong drink let alone squealing on them about a murder. (Along those lines, I've always wondered why the cop in the bar doesn't hassle the Rosatos. You mean to tell me that a beat cop in that neighborhood doesn't know who the Rosato brothers are?)

Anyway, regarding the dynamics between Roth and Mike. Yes, Roth was going to kill Mike from day one. Through Ola he compromised Fredo and he backed the Rosato brothers against Pentangeli. Why? Because Pentangeli ran what used to be the Corleone family which, I guess, Joey Zasa eventually took over. Remember, the Rosato brothers were probably based on the Gallo brothers who rebelled against the Profacis (Clemenza) and then Joe Magliocco (Pentangeli) on behalf of Gambino and Genovese(both Roth)whose real target was Bonanno (Corleone). So, anything that created havoc in the Corleone world Roth perceived as benefiting him.