Ignoring the logistics of the trade, Dubas wouldn't replace Muzzin and Sandin with Chychrun. Leafs need two D-men under team control for the next two years, and Holl's expires next year and will need a raise. They also need Muzzin's long-term replacement and chances are they won't be able to afford Chychrun after the 3 years, so still would need a Muzzin replacement. They have Niemela and other prospects but they might not be it. They also would rather have 4 solid guys in their top 4 rather than 3.

If they can sign Sandin at 2m or lower, then the next season they can move out Muzzin and bring in Chychrun if he is still available. If teams don't give in to Arz's current demands this off-season, Chychrun is likely going to be traded around deadline or next off-season before July 1st when Arz will likely be more eager to move him. Worth noting that Chychrun's 10 team M-NTC kicks in, he's from Florida and been playing in Arizona, so he might block all Canadian teams except Vancouver and 4 other US-based teams.

Agree with you on need to replace Muzz, hence - a different approach by Dubas, keeping space similar to how Colorado did last year, and he can work around the edges to create space (send Mete, Malgin and/or Simmonds down) and add a value LD at the deadline that can play top four minutes. The reason I thought this could work is because it really solidifies the right side which has been a long standing problem for the Leafs. Finding Muzzin's replacement is much easier than filling the right side. Keefe also loves Holl, and Brodie being freed up to play with him stabilizes the second pair. The challenge with hanging on to Muzzin is that if he goes down with an injury you really have no one to play in the top four.

Chychrun is actually just born in Florida, he's from Ottawa. Assuming his parents are just snowbirds.