It's probably 'fair' but I sure wouldn't do it.
Need Vilardi's age and salary control. Toews will be 30 and looking for a payday.
On the pro side, the Kings would trade a player from a position of abundance for a player that would fill a giant hole, especially if Gavrikov doesn't sign. Blake can certainly fill out a deeeeeep forward line-up without Vilardi, but the LHD remains a problem.
Devon Toews is good on both ends of the ice, sporting the highest relative even strength goals for % in the league amongst defensemen (>2000 minutes played) over the past three years. Stanley Cup Champion last season, very good in the playoffs as well. His AAV is only $4.1M next season. Awesome under the radar player.
If the Kings make a one for one trade and don't sign Gavrikov, they could ice a team like this without cap problems:
Iafallo/Fiala-Kopitar-Kempe
Fiala/Iafallo-Byfield-Kaliyev
Moore-Danault-Arvidsson
Grundstrom/JAD-Lizotte-Kupari
Anderson-Doughty
Toews-Roy
Clarke/Spence/Durzi/Walker
Copley/Korpisalo
Dynamite. Of course the Kings could just trade Durzi and Walker for picks and sign Vilardi and Gavrikov. That would be the preferable route.