I have a feeling Kane and Toews will play out their time in Chicago but for different reasons. Besides needing trade waivers from them, the Hawks would have to eat a pile of their $10.5 mil NMC contracts contracts to make a deal ahead of their contract expirations. There are limited trade partners available so unless a team is desperate, it can be tough to make a good deal.
Without some sort of deal, I'd guess that Kane would test the waters in free agency with a contender once he's done here. He still has value as a player and by waiting things out, he'd have more choice$ so I see no reason for him to leave early.
As far as Toews, he might not have enough gas in the tank or fire in the belly to continue on after next year. With last year's time off and his production decline, he'd have a tough time getting top buck as a free agent. With his history of concussions, he might be happy with his savings and whatever he might be able to earn as a non-player and be happy to retire.