Hjalmarsson and Kruger would be amazing additions to the Leafs. Hjalmarsson while not offensively described as a top-pairing guy, he is a top 5 defensive D-man who can constantly allow for the Leafs youngters (and currently other Hawk defenceman) to play in easier situations. He wouldn't be miscast in Toronto (outside of by idiot fans) because Babcock would know his true value and how to use him. Kruger is essential for the Hawks, he allows guys like Kane and Panarin to start in the offensive zone nearly 70% of the time, and for Toews to have very balanced usage. The guy takes a ridiculous amount of defensive zone starts and is a great penalty killer. He consistently wins the small battles and flips the ice.
While the Hawks could use a good LW like JVR, you don't trade two pieces that are so essential in making life easier for you star players. Whatever JVR does to make Toews life easier offensively, will be limited by the increase in tough defensive situations he has to play in due to the loss of Kruger. Or the tougher minutes one of Seabrook or Keith are going to have to take on with the loss of Hjalmarsson.
Leafs also get older, but in a deal like this, I wouldn't mind it, I just can't see it making sense for Chicago. Leafs have 3 defenders in their early to mid-20's who look like top 4 guys. Hjalmarsson would stabilize it. We also aren't doing it by trading significant futures.