Confirmed in 1.5.1 . If a tamed wolf is "angry with"/"attacking" another player, the tamed wolf will remain angry indefinitely. That is even if players log off and back in, or die from the attacking dog. If angry dog is sitting and all players leave the area (area the size of mob spawning radius), the dog/dogs will de-spawn. I'm guessing since they are angry/attacking, they are considered a hostile mob and are de-spawning as such. It is very difficult to keep tamed wolves for this reason.
Confirmed in 1.5.1 . If a tamed wolf is "angry with"/"attacking" another player, the tamed wolf will remain angry indefinitely. That is even if players log off and back in, or die from the attacking dog. If angry dog is sitting and all players leave the area (area the size of mob spawning radius), the dog/dogs will de-spawn. I'm guessing since they are angry/attacking, they are considered a hostile mob and are de-spawning as such. It is very difficult to keep tamed wolves for this reason.