There is a story about Pope St Gregory the Great. There was someone who he excommunicated when he was an abbot. Even this person showed great contrition, he chose not to lift the excommunication. However after this person died he had masses offered for the repose of his soul and he appeared to him in the glory of Heaven.

As I understand it, excommunication is both a spiritual and a legal penalty.  It is both a spiritual warning to the individual AND a legal "scarlet letter" to warn others not to follow the same path.  It is both an individual penalty and a warning to the catholic community.  The Church's act of banning the individual from certain (but not all) public liturgical functions is a warning/prefigurement to the individual that they will not make heaven unless they repent.
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The fact that some are released from their excommunication after death shows that the judicial aspect of the church moves slowly.  Henry IV obviously repented of his sin before his death and then after he died, the Church held an inquiry into his case, to determine his status.  I'm sure they interviewed his confessor and any other priest who had communications with him before he died.  These priests would've confirmed that Henry repented.  Then, the Church would lift his excommunication, post-death.  The reason why it took so long is due to 1) the middle ages' lack of communication/travel/logistics that we're used to.  2) Any legal process (whether Church or secular) does not happen fast.
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In the case of Pope St Gregory the Great not lifting the excommunication for the abbot, this does not mean the abbot could not be saved.  It simply means that Pope St Gregory determined that he did not want an example where an excommunication was lifted easily or quickly.  He was making an example of the abbot to show that whatever he did, was gravely wrong.  Even if the abbot repented and gained the state of grace, the excommunication would be a spiritual penalty in the sense that it would remind the abbot of his former sin so he would not fall again.  (What was he excommunicated for?  If it was a sin where it is easy to fall again, i.e. fornication with one of the villagers?, then such a non-lifting of the excommunication would be a wise reminder.) 
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Back in the day, the Church had special monasteries and jails for priests, monks and clerics who violated Church laws.  These monasteries were often secluded and penitential.  Maybe St Gregory deemed that this abbot needed privacy and seclusion to save his soul?  Not all excommunications are for heresy or mental errors.  There are many in place for sins of the flesh, drunkenness or even witchcraft.  These latter sins are not as easy to "abjure" since they scandalize the faithful with long-lasting consequences.  Thus the Church must "set an example" when clerics cross such lines.

Comparing an unbaptized person to an excommunicated one is totally wrong.  An unbaptized person, spiritually speaking, has more in common with a pagan than any catholic.  Excommunication would be more like to a person in schism.  The Catholic encyclopedia explains it thus.  Take note that an excommunicated person is cut off from the SOCIAL and PUBLIC aspects of the Church only.  It does not affect his potential to obtain heaven, whereas an unbaptized person has no right to heaven, being he is not a child of God.


Excommunication (Latin ex, out of, and communio or communicatio, communion — exclusion from the communion), the principal and severest censure, is a medicinal, spiritual penalty that deprives the guilty Christian of all participation in the common blessings of ecclesiastical society. Being a penalty, it supposes guilt; and being the most serious penalty that the Church can inflict, it naturally supposes a very grave offence. It is also a medicinal rather than a vindictive penalty, being intended, not so much to punish the culprit, as to correct him and bring him back to the path of righteousness. It necessarily, therefore, contemplates the future, either to prevent the recurrence of certain culpable acts that have grievous external consequences, or, more especially, to induce the delinquent to satisfy the obligations incurred by his offence.

Its object and its effect are loss of communion, i.e. of the spiritual benefits shared by all the members of Christian society; hence, it can affect only those who by baptism have been admitted to that society. Undoubtedly there can and do exist other penal measures which entail the loss of certain fixed rights; among them are other censures, e.g. suspension for clerics, interdict for clerics and laymen, irregularity ex delicto, etc. Excommunication, however, is clearly distinguished from these penalties in that it is the privation of all rights resulting from the social status of the Christian as such. The excommunicated person, it is true, does not cease to be a Christian, since his baptism can never be effaced; he can, however, be considered as an exile from Christian society and as non-existent, for a time at least, in the sight of ecclesiastical authority. But such exile can have an end (and the Church desires it), as soon as the offender has given suitable satisfaction. Meanwhile, his status before the Church is that of a stranger. He may not participate in public worship nor receive the Body of Christ or any of the sacraments. Moreover, if he be a cleric, he is forbidden to administer a sacred rite or to exercise an act of spiritual authority.

Comparing an unbaptized person to an excommunicated one is totally wrong.  An unbaptized person, spiritually speaking, has more in common with a pagan than any catholic.  Excommunication would be more like to a person in schism.  The Catholic encyclopedia explains it thus.  Take note that an excommunicated person is cut off from the SOCIAL and PUBLIC aspects of the Church only.  It does not affect his potential to obtain heaven, whereas an unbaptized person has no right to heaven, being he is not a child of God.


Excommunication (Latin ex, out of, and communio or communicatio, communion — exclusion from the communion), the principal and severest censure, is a medicinal, spiritual penalty that deprives the guilty Christian of all participation in the common blessings of ecclesiastical society. Being a penalty, it supposes guilt; and being the most serious penalty that the Church can inflict, it naturally supposes a very grave offence. It is also a medicinal rather than a vindictive penalty, being intended, not so much to punish the culprit, as to correct him and bring him back to the path of righteousness. It necessarily, therefore, contemplates the future, either to prevent the recurrence of certain culpable acts that have grievous external consequences, or, more especially, to induce the delinquent to satisfy the obligations incurred by his offence.

Its object and its effect are loss of communion, i.e. of the spiritual benefits shared by all the members of Christian society; hence, it can affect only those who by baptism have been admitted to that society. Undoubtedly there can and do exist other penal measures which entail the loss of certain fixed rights; among them are other censures, e.g. suspension for clerics, interdict for clerics and laymen, irregularity ex delicto, etc. Excommunication, however, is clearly distinguished from these penalties in that it is the privation of all rights resulting from the social status of the Christian as such. The excommunicated person, it is true, does not cease to be a Christian, since his baptism can never be effaced; he can, however, be considered as an exile from Christian society and as non-existent, for a time at least, in the sight of ecclesiastical authority. But such exile can have an end (and the Church desires it), as soon as the offender has given suitable satisfaction. Meanwhile, his status before the Church is that of a stranger. He may not participate in public worship nor receive the Body of Christ or any of the sacraments. Moreover, if he be a cleric, he is forbidden to administer a sacred rite or to exercise an act of spiritual authority.

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The comparison was to a catechumen (not just any "unbaptized person") specifically, and the scope of the comparison was limited to their relationship to the Church vis a vis membership; obviously since it is a comparison, like all comparisons, there will be other differences.  But the comparison was used by Bellarmine so I feel safe using it myself.