Hainsey is having a good season but is 37. He's gone at the end of the year to clear cap room I'm guessing. Leafs obviously can't sign all of Matthews, Marner, Kapanen, and Gardiner for next year with Nylander's contract. Liljegren or Sandin or both are expected to be on the team next year. Or Rosen or Borgman. That's the plan to make the cap work. Will our D be better? Probably not. Not initially anyway. It may even be worse until the rookies get some experience.
What do we do with Zaitsev? Not sure. He's not really a liability defensively, but he has a 7-year contract because he supposedly can move the puck and contribute offensively. He's probably breaking some kind of Leafs record for the massive drop off in production. Someone needs to light a fire under him. The only way we move that contract right now is by throwing in picks and/or prospects.
I have a feeling all of us (fans) and the media will be complaining about our weaknesses on D for the next couple of years. If we can convince the Blues to part with Pietrangelo without subtracting from the current team, ok great. That's a game-changing trade for the next couple of years. Marleau or Nylander would have to be traded for next season to make that work though.