I can't believe how set the Bruins are on defense. I was not sold on Clifton until recently but I can't deny it anymore, he's legit.
So on RD -- which is the hardest position to fill, you have McAvoy, Carlo, Clifton, Miller. You can trade Miller or rotate all four next year until you hit an injury but they're basically set forever. Kampfer is obviously gone.
On LD -- Chara, Krug, Moore, Gryz, Vaakanainen, Zboril, Lauzon. Chara is back for another year and you can use injuries to test and develop those three prospects. After that, you're in a tough spot if Chara isn't ready to quit. I believe they should keep him if he can maintain his current level of play. He's a defensive rock, the best captain in the NHL and like another coach for the young guys. You also have to decide whether or not to keep Krug and that's another tough call. In any case, there is no wrong answer.
Eventually Seattle comes and takes a player before the 2021-22 season. You just have to live with that, unfortunately.
But any way you slice it, this is the best situation for the Bruins defense in the cap era, if not longer.