Moe's statement has always puzzled me - it sort of implies that he knows he's going to be muscled out or in-on by somebody - otherwise, why must he talk to Barzini about "the deal" if he refuses Michael?

For protection alone, maybe - but why would Barzini rekindle a war for the sake of Moe Green?

I doubt the answer is that Moe knows about the future Barzini move against the Corleone's when the Don dies