I've noticed many times, that when reading a sequence of comments, some of them don't make any sense. It happens if someone delete his comment, and replies to it become meaningless. The recommended approach is to manually flag the dependent comments for deletion by moderator. However, people are not aware about this process (or don't bother to do so).
It will be good to have a reminder for this.
If user deletes the comment that is not the last in the list for question/answer, a popup should appear:
"There are more recent comments, that may depend on your deleted comment, and will be meaningless after the deletion. You can flag individual "broken" comments for review and possible deletion by moderator. Or, if you see it applicable, flag all comments created after deleted one . Do you want to flag all newer comments to be considered for "cascade delete"?"
(suggestions for different wording are welcome)
If the user answers "yes", the chain of subsequent comments will be flagged as "possibly obsolete".
Update: how it can be implemented.
I've got comments, that it will be hard to implement. I think that experienced jQuery developer can do it within a day.
// If a user clicked "delete a comment" icon,
// Check is it the last comment
// If not the last, show the prompt.
// If the use select "flag all newer comments", submit requests to moderator
// for each newer comment with reason "obsolete"
// ( or some new reason, e.g. "Cascade delete")
As an example, how similar task works with a list of comments , see Reply to comment user script
The issue concerned different people, see related suggestions::