Because you gave no details about the system, I quess its a big enough tank to keep a sailfin and I beleive the aggression should end soon.
A torn fin will heal quickly if the fish is healthy and the agressision stops. I would be more conserned about the tang getting ICK from all the stress than the torn fin. Hopefully the tang was QTed to allow it to regain its health befor adding it to your display.
Most any established fish will show some amount of agression or displeasure to new comers and the health of the new comer is very critical befor adding. Most agression with compatible species only last a few hours to a few days. The Spotted hawk is a pretty agressive fish but hopefull they will soon come to terms but if the tank is too small then it could be a never ending issue. Or ending in a bad way......
