Dubas has to bring in a Top 4 D man. He has to.
Rielly and Muzzin are out long term and Brodie's oblique isn't responding as quickly as they'd hoped. That's 3 of your top 4. Can't realistically expect Sandin, Lilly, Holl, and Giordano to fill in. Gio is 39. Holl is Holl. Sandin and Lilly have talent, but are both young and still need to be shielded from facing the opposition's Top lines. They're just not ready for that kind of responsibility.
Maybe they can prove me wrong, but I don't this they can risk it.