I can understand this request very well. Just these days a friend accidently deleted a full chat. He thought that there is an “undo” function (like WA). But it isn’t.
Unfortunately he has no backup too!
Now it would be very welcome and useful to reload (at least) the existing messages from mailserver (a kind of undo).
I think there are more people who will run into such an accident and because the backup/undo/reload issue needs to be described more clear I will open a new FR for that.