Personally I think the biggest need on this team, besides any off-the-wall moves like signing Carlson or Tavares (stating the obvious) is:
Finding a Bozak level replacement for the #3C role. I guess it could be filled by resigning Bozak himself but I think Lars Eller is the best obvious, and potentially cost-saving fit. Backlund is also a stretch option as well, depending if we want to pinch pennies at that spot. If I'm building a team in today's NHL, I'm building it top 9 heavy up the middle->defense and outwards.
Dermott likely graduates next year. Can't see the Leafs overgrooming him for a 2nd year straight. Carrick has been more than adequate at the #3 RHD role, I've been as hard as anyone on him last year- but his play has taken a step up this year. He's noticeably anchoring that pairing, while Borgman has looked awful in spurts IMO. Unless you get a cheap stop-gap, reclamation type like Petrovic- you probably leave that situation open for training camp........and see if one of the bigger D's in the pipeline grab a spot down the line, if size is indeed a pressing concern downstream.