As far as I know halon (which we still have an exemption to use aircraft) is a clear gas and should have no effect on the parts of the engine it contacts. It won't have gone down the core (that bit is supposed to be on fire anyway) but is discharged into the spaces within the cowling where the ancillary drives, pumps and piping etc. are housed. The halon will not damage the aircraft but will rise to the upper atmosphere were it will help to further damage the ozone layer.