Sometimes it is appropriate to delete your own answer or question. That is often because someone explained a problem, and one accepts that the question or answer is not valuable. That is not directly related to down voting - an answer may be well liked, but not actually applicable.
When I agree to delete it based on the comment, I would typically like to reply to the comment - just before deleting the post. This comment I write is associated with that deleted post, and becomes unavailable with it. But that does not mean it is immediately completely lost.
I write that comment not to have it permanently associated with the question or answer, but to reply to the comment that convinced me to delete the post. It is typically to roughly explain my reasoning - or just thanking for the hint by explaining that I learned something from it.
All that is relevant to me is that the recipient (indicated by @) can somehow read the comment - even if it does not become permanent. It could appear in the inbox - and would be visible in part there - truncated to fit the space. Does the notification stay in the inbox even if the associated post is deleted? Can it still be read in full?