May he rest in peace.
As Evelyn Waugh makes clear in “Brideshead Revisited,” divorce and remarriage is a far more serious sin than an occasional affair, because it is harder to repent. The sinner has assumed conflicting obligations that are impossible to resolve.
True repentence includes the determination not to repeat or continue the sin in question. The sinner may fall again, but at the time of confession he must be resolved to fight the temptation as best he may. So the tangled situation of someone who has accepted an obligation to a second wife that is, however, sinful, is very difficult.
This problem can be resolved if the improperly married couple resolve to refrain from any further sexual acts together and to live chastely. Presumably this is what Pavarotti and his second wife—not a true wife in the eyes of the Church—agreed to.
If so, then having his second wife attend the funeral would be legitimate, I believe. Christian charity does not demand that he should throw her off and never see her again, only that they should refrain from further consummating their non-marriage.
Requiescat in pace.