Short answer. No. Article 1276 only extinguishes a guarantor's own liability when merger happens in the principal debtor or creditor, benefiting the guarantor. Confusion happening in the guarantor's own person, as in your case, does not extinguish the main obligation between the principal debtor and creditor.
What the law says
Merger which takes place in the person of the principal debtor or creditor benefits the guarantors.
Civil Code, Article 1276 — Confusion and Guarantors. Read the full provision →
What the law says
Confusion which takes place in the person of any of the latter does not extinguish the obligation.
Civil Code, Article 1276 — Confusion and Guarantors. Read the full provision →
Merger runs one direction, not the other
Article 1276 draws a careful distinction based on whose roles actually merge. The first rule favors the guarantor: "merger which takes place in the person of the principal debtor or creditor benefits the guarantors." If the principal debtor and creditor became the same person, the main obligation is extinguished, and because a guarantee is only as strong as the obligation it secures, the guarantor is released too. But this rule is about merger happening between the principal parties, not the guarantor.
Why your situation is different
You did not become both the principal debtor and the principal creditor — you became the creditor's heir while remaining a guarantor, not the debtor. The article's second sentence covers exactly this scenario: "confusion which takes place in the person of any of the latter does not extinguish the obligation." "The latter" refers to the guarantors just mentioned in the same article. So merger occurring in a guarantor's own person, rather than between the principal debtor and creditor, leaves the underlying obligation standing.
What this means practically for you
As the creditor's heir, you may now hold the creditor's right to collect from the principal debtor, but that is a separate question from your own liability as guarantor. The principal debtor's obligation to pay does not disappear just because you, the guarantor, inherited the creditor's position. If anything, you may now be positioned to collect from the principal debtor directly, since you have inherited that right, while your own guarantee obligation is unaffected by the merger that happened only in your person.
The underlying logic of the rule
The rule protects the principal obligation from being wiped out by something happening to a secondary party like a guarantor, since a guarantee is meant to add security for the creditor, not to create a loophole that extinguishes the debt whenever a coincidence of roles occurs on the guarantor's side. Extinguishing the guarantor's own liability when merger happens between the principal parties makes sense, because the debt itself is gone; but letting a guarantor's personal circumstances erase the principal debtor's obligation would undermine the whole purpose of requiring a guarantee in the first place.