Short answer. It may be void. Article 2023 makes a life annuity void if it is constituted on the life of someone already dead when the contract was made, or someone then suffering from an illness that caused his death within twenty days of that date. Death after that window does not invalidate it.
What the law says
Life annuity shall be void if constituted upon the life of a person who was already dead at the time the contract was entered into, or who was at that time suffering from an illness which caused his death within twenty days following said date.
Civil Code, Article 2023 — Void Life Annuity. Read the full provision →
The gamble has to be real
A life annuity is an aleatory contract — a genuine wager on how long a life will last. If the measuring life is already gone, or so close to its end that the outcome is effectively settled, there is no real chance to bet on, and the contract loses the uncertainty that gives it legal footing. Article 2023 turns that principle into a hard rule: Life annuity shall be void if constituted upon the life of a person who was already dead at the time the contract was entered into, or who was at that time suffering from an illness which caused his death within twenty days following said date.
Two situations, one of them measured backward
The article voids the annuity in two cases. The first is straightforward: the measuring life was already dead when the parties signed. The second is the one your question raises: the person was, at signing, suffering from an illness — and that same illness then caused his death within twenty days. Note that this test is applied looking back from the death. It is not enough that someone was gravely ill; the illness present at signing must be the one that killed him, and death must fall inside the twenty-day window running from the date of the contract.
Surviving the window saves the contract
The twenty-day period is a bright line. If the measuring life, however sick at signing, lives beyond twenty days, the annuity is not struck down by this article — the required uncertainty is treated as having genuinely existed. So a person who was terminally ill at the outset but lived twenty-one days, or several months, leaves a valid contract behind. The rule does not ask whether the parties knew of the illness; it fixes on two objective facts, the presence of the fatal illness at signing and the timing of the death, and lets those facts decide.
What decides it, and what follows
If a measuring life dies very soon after the annuity is set up, the decisive evidence is the person's medical condition at signing and the cause and date of death — so the contract date and the medical records are what a dispute will turn on. Where the annuity is void under this article, it produces no valid obligation: no pension is owed, and the parties are returned to their former positions as with any void contract, the capital no longer resting on a bargain the law recognises. Establish the health facts early, because everything here follows from them.