Short answer. Yes. Article 766 provides that alienations and mortgages made before the notation of the revocation complaint in the Registry of Property shall subsist, even though the donation is revoked for ingratitude. Because the sale happened before your complaint was recorded, the buyer's title is protected.
What the law says
Although the donation is revoked on account of ingratitude, nevertheless, the alienations and mortgages effected before the notation of the complaint for revocation in the Registry of Property shall subsist. Later ones shall be void.
Civil Code, Article 766 — Effect Of Revocation On Third Persons. Read the full provision →
Timing relative to the notation is what decides the outcome
Article 766 draws the line precisely where your question is asking about: although the donation is revoked on account of ingratitude, nevertheless, the alienations and mortgages effected before the notation of the complaint for revocation in the Registry of Property shall subsist. Revocation for ingratitude does not automatically undo everything the donee did with the property beforehand. A sale executed before your complaint was annotated in the Registry of Property is protected and remains valid, even though the underlying donation is later revoked.
Why the notation date, not the filing date, is what matters
The protection Article 766 grants runs specifically from the moment the complaint for revocation is noted in the Registry of Property, not from when you first decided to revoke the donation or even from when you filed the case in court. Until that notation appears in the registry, a buyer dealing with the donee has no public record indicating the donation is under attack, and the law protects transactions made in that window rather than exposing every prior transfer to being unwound once revocation is eventually granted.
What changes once the complaint is annotated
The article draws a sharp contrast for what happens afterward: later ones shall be void. Any alienation or mortgage the donee attempts after your complaint has been noted in the Registry of Property is void, meaning the registry entry functions as the dividing line between transactions the law protects and transactions the law refuses to recognize. This is why promptly annotating a revocation complaint matters: it is what starts protecting you against further transfers by the donee.
What this means for your revocation case
Since the sale you describe happened before your complaint was recorded, the buyer's acquisition of the land generally subsists despite the donation being revoked, and your revocation will not by itself undo that particular sale. Your remedy against the donee for the ingratitude, and whatever value the property represented, would need to be pursued through other means, such as recovering the equivalent value from the donee, rather than by reaching into the buyer's now-protected title to the land itself.