Since the Reply tool knows which comment I'm replying to, why can't it tell me, when I click the big blue button, that someone else has already replied to it while I was typing?
And perhaps more generally, consider telling me before I post that someone else has edited the page in the meantime.
To extract the reasons/description from the broader post, and with some additions:
Currently, the reply tool doesn't give any indication about new changes to the discussion/page since the page loaded (other than a warning/error message either beforehand or afterwards, in case of drastic changes to the page). Within the widget there's no way to figure out if there are any changes before publishing a comment, and the whole page gets updated silently after successfully publishing the comment: any intermediate changes to the page, also in other sections, are updated/'injected' without visual indication (while the just added comment has a fancy fading background color).
(In comparison: when replying using the regular edit page, clicking the "Show changes" button 'warns' of any changes to the section – instantly when the preference "Show previews without reloading the page" is checked.)
As a starting point for this task/request:
After clicking the blue "Reply" button, a note or warning message similar to the 'comment-disappeared' error message could be shown, postponing the publishing process (instead of cancelling like when the replied-to comment disappeared in the meantime). Something like:
Ultimately, something like a 'live' button for updating/injection of changed and new comments would be great, comparable to a news site's live blog. I'm aware that a Wiki talk page is a bit more complicated than a linear thread of news items, but – seeing that publishing a comment with the reply tool already uses some live update of the page, without reloading it – a button to update the page (with e.g. a background color indicating changes and added comments) while the reply tool widget stays open, seems not to be a too far stretch.