Currently, as I see, when a comment is deleted, it leaves no traces of its existence at all. This can lead to somewhat confusing "discussion remains", where a followup comment is not understandable (whereas in reality it was answering a later vanished comment, only you don't have any ideas about that).
Take, for instance, this discussion:
See, 2 + 2 = 5 No, actually 2 + 2 = 4 That's right!
If the second comment is deleted, it turns into this:
See, 2 + 2 = 5 That's right!
Please leave some placeholder in place of deleted comments, so that it can at least be guessed that further comments now lack some context:
See, 2 + 2 = 5 [comment deleted] That's right!