Quoting: Isles10
Mayfield will return a 1st and a 3rd by himself + an RD is the Senators biggest need (he's extended here). Dufour has the value of a late 1st, so essentially three 1st rounders in value for DeBrincat, it's more than they paid for him... this scenario is if they can't come to an agreement by TDL.
Mayfield
may return a late 1st and a 3rd if teams are desperate but there are lots of options for cheap decent defense this year (Schenn, Braun, Maatta retained, Holden, Shattenkirk retained, Gavrikov retained, Gudas retained, Stecher, Kulikov, Walman, Tinordi, etc), so I would say it's pretty unlikely that happens.
Dufour looked solid in the Q but really hasn't been that great in the AHL so far. I would not pay a 1st for him personally, but lets say someone would for arguments sake
To summarize that would be at most 2 late 1st's and a mid/late 1st vs 7th OA, an early 2nd, and a 3rd. Gonna have to disagree with you here.