Objection 1. It would seem that no man can be absolved against his will. For spiritual things are not conferred on anyone against his will. Now absolution from excommunication is a spiritual favor. Therefore it cannot be granted to a man against his will.
Objection 2. Further, the cause of excommunication is contumacy. But when, through contempt of the excommunication, a man is unwilling to be absolved, he shows a high degree of contumacy. Therefore he cannot be absolved.
On the contrary, Excommunication can be pronounced on a man against his will. Now things that happen to a man against his will, can be removed from him against his will, as in the case of the goods of fortune. Therefore excommunication can be removed from a man against his will.
I answer that, Evil of fault and evil of punishment differ in this, that the origin of fault is within us, since all sin is voluntary, whereas the origin of punishment is sometimes without, since punishment does not need to be voluntary, in fact the nature of punishment is rather to be against the will. Wherefore, just as a man commits no sin except willingly, so no sin is forgiven him against his will. On the other hand just as a person can be excommunicated against his will, so can he be absolved therefrom.
Reply to Objection 1. The assertion is true of those spiritual goods which depend on our will, such as the virtues, which we cannot lose unwillingly; for knowledge, although a spiritual good, can be lost by a man against his will through sickness. Hence the argument is not to the point.
Reply to Objection 2. It is possible for excommunication to be removed from a man even though he be contumacious, if it seem to be for the good of the man for whom the excommunication was intended as a medicine.
Source: Summa Theologica (New Advent)