I think its best to assume that were the proud recipients of an exterminatus and simply destroyed although there is no offical cannon on this.
After the heresy all records of the traitors were expunged from all records and any proof was destroyed. Including the complete destruction of all traitorous homeworlds.
In current 40k the offical line is that chaos does'nt exist it says at the start of codex CSM that the inquisiton ensure that no record of chaos incursions or existance is allowed to exist.
Chaos one of the best kept secrets of the 40k galaxy