Short answer. Yes. Article 801 provides that supervening incapacity does not invalidate an effective will. Capacity is tested at the moment of execution and at no other time, so an illness that arrives afterwards, however severe, leaves a validly made will standing.

What the law says

Supervening incapacity does not invalidate an effective will, nor is the will of an incapable validated by the supervening of capacity.

Civil Code, Article 801 — Supervening Incapacity. Read the full provision →

One moment governs, and it is the signing

The rule fixes a single point of assessment. If your father understood what he was doing when he executed the will, the will is effective, and nothing that happened to his mind afterwards touches it. That is not a technicality but a necessity: wills are commonly made years before death, often precisely because the testator can see decline coming, and a rule that reopened capacity at the date of death would make every considered will worthless in the cases where it is most needed.

The rule cuts both ways

The second half of the sentence is the mirror image and is easy to overlook: nor is the will of an incapable validated by the supervening of capacity. A will executed by someone who lacked capacity is void then and stays void, and recovery does not cure it. The document has to be executed again, with the formalities, while the testator is capable. Families sometimes assume that a period of clarity after a bad episode retroactively repairs a document signed during it. It does not, and the fix is a fresh will, not an affidavit.

What incapacity after execution really costs

The practical loss is not the will but the ability to change it. Once capacity is gone, the testator can no longer revoke the will, execute a codicil, or adjust it for a birth, a death, a sale or a falling-out. The document is frozen in the circumstances of the day it was signed, which is why a will drafted years earlier can distribute an estate that no longer resembles the one described in it. Property acquired after the will was made raises a separate question of its own.

Where the fight will actually be

Because a later stroke is irrelevant, an opponent of the will has to attack the execution itself — arguing that the decline had already begun, that the will was signed during an earlier episode rather than before it, or that someone exerted pressure. So the evidence that matters is dated: medical records from before and around the signing, the recollections of the attesting witnesses, and who arranged for the will to be drawn. Establish the date of the will against the date of the stroke first; if the order is clear, most of the dispute closes with it.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.