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There are some good reasons to prevent question deletion when answers exist. There are users that believe the correct course of action is to "clean up" their instance of communication on the site, by deleting their question, once they have received a question. This is wrong, and the system should have measures in place to prevent this. Simply eternally preventing self-deletion once an answer exists, solves this problem.

Additionally, question deletes is a demotivating factor for an answerer. Answers are posted to help not just the author, but everyone that comes after. Time and effort is put into them, and it's discouraging to have your content involuntarily removed.

That said, preventing self-deletion is also an issue. There are cases in which the question author later comes to the realization that their question is of low quality, and should be removed. This is now impossible, if somebody made the bad decision of posting an answer to this question. I am not sure how much of an issue this is on Codidact, but it's a considerable problem on Stack Overflow. One of the things often encountered, is people that constantly answer obvious duplicates, or other low-quality contributions, many of them worthy of closure. I have been in this situation myself; years ago, I posted some bad questions on SO, as a beginner in the field of programming. I quickly received bad feedback, but was unable to clean up my mess, because several answers were already posted. There were also examples of questions where I came back a few years later, and tried several methods of getting them deleted. Still not having deletion votes, I had to ask in chat rooms for support; my requests either went unnoticed, or were banned (requests with self-involvement are prohibited in SOCVR, for instance). Most new users don't even know about these opportunities. Users need to have realistic and easy ways to clean up their own mess once they realize their own mistakes.

Preventing deletion due to comments, magnifies this problem significantly. Comments are not for answering, but for clarifications, critique, or other similar uses. For instance, pointing out how a question is off-topic, or guiding a user about the rules, are accepted uses. So preventing deletion due to comments is not a fine measure.

I think a possible solution to your issue, would be to let users view deleted posts that they have interacted with. That is however a suggestion in need of further scrutiny, and outside the scope of this answer. 

Conclusion: preventing deletion due to comments? Absolutely not. Due to answers? Only if the user is still given appropriate and accessible ways to clean up their questions in the case that they are indeed inappropriate for the site, and the answers were posted in the wrong.