Doesnt hurt to expel him from the party and strip him of his pension. We have done that to other members of Politburo in the past. I'm assuming CCDI is already on this. Hopefully the investigation concludes shortly and we hear an outcome.
It's a matter of proportionality. Having an affair in no ways justifies expulsion from the party.
Look, Xi offered a deal years ago. Don't do new shit and I'll let old shit pass. Going after retired officials for past affairs breaks the bargain.