That 3rd line just doesn't look good, Namestnikov can't carry lesser players, would keep Gourde there as he gets more out of people.
As for the D those pairings are fine, Sustr is fine when he plays with Coburn and vice versa. As for looking for a defensive upgrade Girardi seems like the one but they aren't dropping him, they're bump Sustr. The only issue is Green as a partner for Sergachev isn't good and they seem to not want to put Sergachev on the right so another LD makes no sense.