You can fix this as long as the core's integrity isn't compromised. If you can, get some heavy duty pliers (lineman's pliers, I believe) and pull on the tab closest to the dent outwards. This should straighten the fins out. You still might have to tweak it a little for the tabs to line up for mounting the IC, but it should be ok. We run into this all of the time where I work and that's what we do to fix them.
Granted, the cores that we fix aren't as thick as that IC is, but the above mentioned method works pretty well.
My car is well, it's like 10 lbs of shit in a 5 lb bag...
<------ Click to see what I'm workin' with. ;)