As far as I know, deleted comments cannot be restored, so this implies that comments are not stored after a deletion and possible the comment doesn't leave any data in the database.
In order to retrieve comments and historic data, you will need to retrieve database backups.
Another thing you can do is to create a notification for deleted comments on a specific task.
But this needs to be set manually for each issue... But may exist something automatically ( which I don't know ..yet),
This is the view of my Notification helper, maybe in for Trello looks different.
If you had to thrive a new habit during a lockdown, what would it be? Trello
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event