This is a very interesting question. I am going to give a quick answer for the time being.

(1) The Ritva at the bottom of 11b asks on the opinion of the Gemara there ("Mesah Kehunah") that when the Kohen Gadol is proved to be the son of a divorcee this is considered equivalent to the K.G. dying (i.e. the KG is only considered invalid from now on but not retroactively) :- how can one compare the KG dying to the KG being invalidated? We know that when the KG dies this is a Kapara and the crime of the murderers is atoned for and they may therefore go home, but where is the Kapara when the KG is merely proved to be a Chalal, an invalid Kohen?

(2) The Ritva answers that the pain suffered by the KG when they found out about his pesul, is equivalent to him dying. The anguish that he suffers through losing his lofty position and the embarassment he sustained, is also sufficient to be "Mechaper".

(3) According to this it would appear that even if the KG was afterwards re-instated - because the eidim who invalidated him were themselves invalidated - nevertheless the pain that the KG suffered at the time of his original disgrace, cannot be erased. Therefore the Rotzeach received his Kapara and he does not need to return to the Ir Miklat, and the Go'el hadam has no right to kill him.

Thanking you again for this fascinating question

KOL TUV

Dovid Bloom

Follow-up reply:

I found an important source who elaborates on the above Chidush of the Ritva. According to this my original answer may not be correct.

(1) The source is the Dvar Avraham 1:26:8 DH Aval (written by Rav Avraham Duber Cahana Shapira, the last Rav of Kovna before and during the Holocaust). The Dvar Avraham points out that the Ritva's svoro appears to be very strange. How can one possibly say that because the Kohen Gadol suffers pain this is considered equivalent to dying? Is it at all posible that if the KG suffered some other kind of pain (for instance a severe financial loss) that this would also be equivalent to him dying?!

(2) To solve this paradox, Dvar Avraham explains that in fact in the standard case where the KG dies there are 2 factors that enable the Rotzchim to go free (a) the sorrow caused by the death of the KG which serves as a kapara (b) the fact that there has been a break in the position of the KG because after he died he clearly is no longer the KG. If only one of these factors exist the Rotzchim do not go free, which answers the Dvar Avraham's rhetorical question mentioned above in (1), since the KG suffering pain can only set the Rotzchim free if in addition the KG also loses his job.

(3) According to this, if the KG is proved to be the son of a divorcee both (a) and (b) are fulfilled :- (a) is fulfilled because of the pain caused to the KG by his disqualfication and (b) is fulfilled because his officiating as KG has been ceased by his disqualification. However if afterwards the witnesses who disqualified the KG are themselves proved to be thieves etc., even though the KG experienced (a) since his demotion caused him anguish equivalent to death, nevertheless after the KG was re-instated one can argue that (b) was not fulfilled because even though his position was temporarily lost, on the other hand later on he received his rank back. Therefore even though the KG suffered terrible embarassment when he was disqualified, his position as KG was not cut off, and it should follow that this is not equivalent to the KG dying and the Rotzchim do not go free.

KOL TUV

Dovid Bloom