I'm a huge fan of the team the Blues have assembled, they've been patiently putting together a powerhouse for a while and the only real piece they're missing is an offensive catalyst which may one day be filled by Tarasenko.
But as for Halak, I can't really think of any valid reasons why they'd trade him. He's young, a good goalie, a proven playoff performer, and they gave up quite a bit to get him in the first place.