Vito played his last moments so beautifully. Keeping the inner circle so tight to flush out any last minute traitors or members who failed to stay loyal during the Corleone's appearance of their "weakest times".

Tessio was probably expecting a large pay out and disappear if his intel was provided correctly and the hit on Micheal was successful. Clemenza would eventually be a target too. Turnbull is correct about Barzini keeping a traitor around from Don to another which would make Tessio disappear fast.