The premise of this question is flawed. You seem to believe that your placeholder answer would prevent the question from being closed or deleted, and that is not generally true.
The OP of a question can choose to delete their own question (together with your answer) at any time until one of several criteria are met to block that action. (See How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion?). It could be that something about the circumstances of when you posted your stub would have triggered one of those, but generally speaking one would hope that there are not a lot of answers going onto questions that are getting as heavy negative feedback as you've suggested for at least one of the questions that you references in comments nor upvotes on a stub that doesn't (yet) provide a real answer.
Moreover, if you expected the question to be closed, which can happen even if answers are already posted, then roomba could well delete the question and answer in as few as 9 days depending on how many votes are cast.
Either way, your answer stood a chance of being deleted sooner or later if the question had serious problems. (And if it didn't then the stub was unnecessary by any measure.)
Beyond the technical points, what you're doing with the stub answer is trying to circumvent both the SE software and the other users on the site. Provided the question had issues that justified your concern about deletion or closure, then it would seem that you
- Realized that the question had problems;
- Realized that other users also saw the problems are were providing feedback including downvotes and/or close votes; and
- Feared that the OP of the question would act on that feedback by deleting their question.
A primary purpose of downvoting a question is to induce the poster to delete it. (Related: https://stackoverflow.blog/2011/06/13/optimizing-for-pearls-not-sand/) That's why SE refunds the reputation lost on delete posts - Part of the "don't hold a grudge" approach taken by the site for users who correct their mistakes. In addition to trying to keep a question that you evidentially thought was poor on the site, if you had been successful you would also, as side effects, have:
- Negated what you saw as the community's overall response to the question; and
- Prevented the OP of the question from deleting their question, which then would expose them to more negative feedback rather than allowing them to gracefully back out, perhaps to regroup and post better later.
If you really thought the question was salvageable, then the appropriate recourse would be to fix the question first not to provide an answer to a question that even you (apparently) thought had significant issues.